Will the Stone Pass on Its Own? How Size and Location Decide Kidney Stone Treatment

The scan is up on the screen and the radiologist’s note is only two lines long: a stone, a measurement in millimeters, and a location somewhere along the narrow tube between kidney and bladder. You are lying on an emergency department bed at three in the morning, the worst of the pain finally dulled, and the question forming is not about anatomy. It is simpler than that. Will this thing come out on its own, or is someone going to have to go in and get it?

That question has a surprisingly structured answer. Urologists asking when do kidney stones need surgery are really asking two things: how big is the stone, and where is it sitting. Add a third factor, whether anything dangerous is happening around it, and you have most of the decision tree.

What follows is that decision tree in plain language: what tends to pass, what tends not to, what each procedure actually involves, and which signs mean the waiting is over.

What decides whether a kidney stone passes on its own?

A kidney stone is a hard clump of minerals, most often calcium oxalate, that crystallizes out of concentrated urine inside the kidney. While it stays in the kidney it may cause nothing at all. Trouble begins when it drops into the ureter, the muscular tube roughly as wide as a cooked spaghetti strand that carries urine to the bladder. The ureter squeezes rhythmically to push urine along, and a stone caught in that squeeze is what produces the famous wave-like pain.

Three things then govern the outcome. The first is diameter. The ureter can stretch, but only so far, so a stone’s width relative to that tube is the single strongest predictor of whether it will keep moving. The second is position. A stone that has already traveled most of the way down has fewer obstacles ahead than one lodged near the kidney. The third is what the stone is doing to the system behind it: how much urine is backing up, whether infection has taken hold, and whether the person has a second healthy kidney doing the work in the meantime.

The encouraging part is that these factors line up in favor of watchful waiting far more often than not. The NHS notes that most kidney stones are small enough to pass in the urine, often with pain treated at home, and that stones causing discomfort usually clear within days to a few weeks (see the NHS reference). The less comfortable part is that “most” is not “all”, and the exceptions are exactly where urologists earn their keep.

At what size do kidney stones typically require surgery?

Size is measured on a CT scan or ultrasound in millimeters, and small differences matter more than they sound. The NHS puts the practical threshold at around 6 to 7 mm: stones at or above that diameter are considered too big to pass naturally and are the ones most likely to need a procedure (NHS). Below that line, the odds of spontaneous passage rise sharply as the stone gets smaller.

Picture the scale. A 3 mm stone is about the width of a grain of rice. A 6 mm stone is closer to a pencil eraser. A 10 mm stone approaches the width of a fingernail, and a stone of 20 mm or more, the size where the NHS describes percutaneous surgery as the usual approach, is more like a marble sitting inside an organ roughly the size of a fist (NHS).

Two cautions keep this from becoming a simple kidney stone size chart for surgery. First, radiology measurements have margins. A stone read as 5 mm on one scan can be reported as 6 mm on another, so clinicians treat the number as a strong signal rather than a switch. Second, size only tells you the likelihood of passage, not whether waiting is safe. A 4 mm stone accompanied by a fever demands urgent attention; a 9 mm stone sitting quietly in the kidney, causing no blockage, may be watched for a long time. Size sets expectations. The rest of the picture sets the plan.

Why location matters as much as size

Two stones of identical diameter can have very different futures depending on where they are. Urologists divide the urinary tract into a few zones, and each behaves differently.

Stones still inside the kidney, resting in the collecting cups called calyces or in the central chamber called the renal pelvis, are frequently silent. Many are found by accident on scans ordered for other reasons. Because they are not blocking anything, the usual conversation is about monitoring and prevention rather than removal, unless they grow, cause infections, or bleed. The Mayo Clinic describes larger treatment being reserved for stones that are too big to pass, cause bleeding, damage the kidney, or trigger ongoing urinary infections (Mayo Clinic).

Once a stone enters the ureter, position along that tube becomes the key detail. The ureter has three natural pinch points: where it leaves the kidney, where it crosses over the pelvic blood vessels, and where it tunnels into the bladder wall. Stones tend to pause at these narrowings. A stone in the upper ureter, near the kidney, has all three ahead of it. A stone in the lower ureter, close to the bladder, has already cleared two and is often within days of passing.

Location also shapes which procedure is chosen if one is needed. Lower ureteral stones are easy to reach with a thin scope passed from below. Large stones in the kidney itself are more efficiently removed through a small incision in the back. When your team says “it depends where it is”, this is what they mean, and it is not a hedge.

Can kidney stones go away without surgery? Observation and medical expulsive therapy

Yes, and for small stones this is the standard first plan rather than a fallback. Conservative management has three components: time, fluids, and pain control, sometimes with a medicine that helps the ureter relax.

Time does most of the work. The ureter’s own contractions gradually move the stone downward, and each pinch point it clears improves the odds. Fluids matter because a steady flow of urine keeps gentle pressure behind the stone; the NIDDK advises drinking enough to keep urine pale unless a clinician has said otherwise (NIDDK). Pain relief matters because uncontrolled pain is itself a reason to abandon waiting, and because a person in agony rarely drinks enough.

The fourth element is a class of medicines called alpha blockers. Originally developed for blood pressure and prostate symptoms, they relax smooth muscle, including the muscle in the lower ureter, widening the passage slightly and reducing spasm. The Mayo Clinic describes them as a way to help pass a stone more quickly and with less pain (Mayo Clinic). Whether they are appropriate, and for how long, is a decision for the prescribing clinician; they are not suitable for everyone, and their benefit is clearest for stones sitting low in the ureter.

Observation is not the same as neglect. It comes with a follow-up plan: a repeat scan or X-ray if the stone has not appeared, and clear instructions on which symptoms end the waiting period. If those instructions were not spelled out, ask for them before leaving the clinic. Kidney stones can pass on their own, but they should do so under supervision.

How long can a kidney stone be left untreated?

This is the question that keeps people awake, and the honest answer has two halves. For a small stone that is causing symptoms but no fever, no infection, and no severe blockage, a few weeks of watchful waiting is routine. The NHS describes symptomatic stones typically passing within days to a few weeks (NHS), and most urologists schedule a check-in within that window to confirm progress.

The danger lies not in the calendar but in what the stone is doing meanwhile. A stone that fully blocks the ureter causes urine to back up into the kidney, a state called hydronephrosis, which is simply swelling from trapped fluid. The kidney tolerates mild swelling for a while, but prolonged high pressure can gradually injure the filtering tissue. The Mayo Clinic lists kidney damage among the reasons a stone may need active removal rather than observation (Mayo Clinic). This is why a repeat scan matters: it checks not only whether the stone has moved, but whether the kidney behind it is still comfortable.

A stone left untreated becomes an emergency the moment infection joins the picture. Bacteria trapped behind a blockage cannot be flushed out, and the combination of obstruction and infection can spread to the bloodstream quickly. Fever with a known stone is never a wait-and-see situation.

Stones resting in the kidney without blocking anything are a separate category. Some are monitored for years with periodic imaging, because the risks of removal outweigh the risks of leaving a quiet stone alone. Your team will tell you which kind you have; the label “untreated” means something different in each case.

When do kidney stones need surgery? The situations that change the plan

Set aside size for a moment. Several circumstances push a urologist toward intervention regardless of the millimeter reading, and they are worth knowing because they explain why two neighbors with similar stones may receive very different advice.

Infection with obstruction sits at the top. When a fever, chills, or signs of a urinary infection appear alongside a blocking stone, the priority is to drain the kidney urgently, usually with a stent or a drainage tube, and remove the stone once the infection is controlled. Waiting here is not an option, and no guideline treats it as one.

Pain that cannot be managed is the second. Some people tolerate a small stone with over-the-counter relief; others cannot function, cannot keep fluids down, or return to the emergency department repeatedly. Repeated visits for the same stone are a practical signal that observation has run its course.

A single functioning kidney changes the math entirely. When there is no backup organ, even a modest blockage carries higher stakes, and urologists tend to act earlier. The same applies to people with reduced kidney function, a transplanted kidney, or anatomy that makes passage unlikely.

Finally, there is failure to progress. A stone that has not moved on follow-up imaging after several weeks is unlikely to start now, and the longer it sits, the more inflamed and scarred the surrounding ureter becomes, which can make later removal harder. The NIDDK notes that a healthcare professional may remove stones that are too large to pass, block urine flow, or cause pain and bleeding (NIDDK). Each of these is a judgment call. Each belongs to the treating team, informed by your symptoms and your preferences.

How do you know if you need surgery for kidney stones? The tests behind the decision

Nobody decides on kidney stone surgery from symptoms alone, because pain intensity is a poor guide to stone size. A tiny fragment scraping through the lower ureter can hurt more than a large stone resting quietly in the kidney. Objective information comes from a short list of tests.

Imaging leads. A non-contrast CT scan is the most accurate way to measure a stone and pinpoint its location, and it also shows how swollen the kidney behind it has become (Mayo Clinic). Ultrasound avoids radiation and is often used first in pregnancy and in children, though it can miss small ureteral stones. A plain abdominal X-ray is sometimes used for follow-up if the stone was visible on it initially, because it is quick and low-dose.

Blood tests check kidney function, measured through creatinine, and look for signs of infection such as a raised white cell count. Calcium and uric acid levels can hint at why the stone formed. A urine test looks for blood, crystals, and bacteria; a culture identifies any infection so it can be treated properly (MedlinePlus).

Then comes the part that no scan can do: a conversation. The urologist will want to know how the pain is behaving, whether you have passed stones before, whether you can drink and keep fluids down, how far you live from emergency care, and what matters to you. Some people prefer a definitive procedure over weeks of uncertainty; others would rather avoid anesthesia if there is a reasonable chance of passing the stone. Both are legitimate. Signs you need kidney stone surgery are read from the whole picture, not a single number.

How kidney stone surgery works: the three main procedures explained

The word “surgery” alarms people, and it helps to know that none of the standard kidney stone procedures involve a large incision. All three described by the NHS and NIDDK are performed under anesthesia, and two of them leave no cut at all (NHS; NIDDK).

Shock wave lithotripsy sends focused sound-pressure waves from a machine outside the body, through the skin, to the stone. Lithotripsy simply means “stone breaking”. The waves shatter the stone into sand-like fragments that pass in the urine over the following days and weeks. It suits stones in the kidney or upper ureter that are not too large or too hard, and the NHS describes it as an option for stones up to about 20 mm (NHS). Bruising over the flank and blood in the urine for a few days are expected.

Ureteroscopy uses a very thin, flexible telescope passed through the urethra and bladder and up the ureter, with no incision. The surgeon sees the stone directly and either pulls it out in a tiny basket or breaks it with a laser fiber first. Because the whole ureter and much of the kidney can be reached, this has become a workhorse for ureteral stones of most sizes. A temporary stent is often left afterward.

Percutaneous nephrolithotomy, usually shortened to PCNL, is reserved for large or complex stones in the kidney itself. The surgeon makes a small incision in the back, about the width of a finger, creates a tract into the kidney, and removes the stone through it. The NHS describes it as the usual choice for stones of 20 mm or more (NHS). It typically involves a short hospital stay rather than same-day discharge.

Which kidney stone procedure for which stone? A comparison

The table below summarizes how the three approaches are typically matched to stones, drawing on the NHS and NIDDK descriptions. It is a map of common practice, not a rulebook; anatomy, stone hardness, other health conditions and your own preferences all shift the choice.

Procedure	How the stone is reached	Typically used for	Commonly discussed drawbacks
Shock wave lithotripsy	Sound waves from outside the body; no incision	Kidney or upper ureter stones up to about 20 mm	Fragments must still pass; may need repeat sessions; less effective for very hard or very large stones
Ureteroscopy	Thin scope through the urethra; no incision	Stones anywhere in the ureter; many kidney stones	Stent discomfort afterward; small risk of ureter injury; sometimes staged for large stones
Percutaneous nephrolithotomy	Small incision in the back directly into the kidney	Large or complex kidney stones, roughly 20 mm and above	Hospital stay; bleeding risk; longer recovery than the other two

A few patterns explain the choices. Shock waves lose accuracy on stones that are hard to target, which is why body build and stone composition matter. Ureteroscopy offers the surgeon a direct view, so it is favored when precision matters or when a stone has resisted shock waves. PCNL trades a small incision for the ability to clear a large stone burden in one sitting.

All three carry the general risks of anesthesia, and all three can leave fragments behind that need a second look. The Mayo Clinic notes that residual fragments and the need for additional procedures are part of the conversation for every method (Mayo Clinic). Ask your team which option they recommend for your specific stone and why, and what the plan would be if the first attempt does not clear it completely.

Who is usually offered a procedure, and who is usually asked to wait

The clearest way to understand the decision is to look at the two ends of the spectrum, then acknowledge the middle where judgment lives.

People commonly offered a procedure promptly include those with a stone at or above the 6 to 7 mm range described by the NHS (NHS), those with a blocked kidney and any sign of infection, those with a single or transplanted kidney, those whose pain cannot be controlled or who cannot keep fluids down, and those whose stone has failed to move on repeat imaging. Certain occupations also tip the balance: airline pilots, for example, are often treated definitively because an unpredictable episode of pain at work could endanger others.

People usually asked to wait have a small stone, often under 5 mm, that is already low in the ureter, with pain that responds to medication, no fever, normal kidney function on blood tests, and a second healthy kidney. For them, the risks of anesthesia and instrumentation generally outweigh the modest benefit of removing something that will likely leave on its own.

The middle ground is real. A 6 mm stone in the upper ureter of an otherwise healthy person could reasonably be watched for a couple of weeks or treated straight away, and guidelines allow both. Here the person’s own priorities carry weight. Someone who cannot afford time off for repeated emergency visits, or who lives hours from care, may prefer certainty. Someone anxious about anesthesia may prefer to give the stone a chance. Neither is wrong, and a good urologist will lay out the trade-offs rather than present a single answer.

What the following days and weeks usually look like after treatment

Recovery depends heavily on which procedure was done and whether a stent was placed, so consider this a typical pattern rather than a schedule.

After shock wave lithotripsy, most people go home the same day. Passing the fragments takes days to weeks, and the urine may be pink or contain visible grit. Flank soreness where the waves entered is common. A follow-up X-ray or ultrasound checks whether the fragments have cleared and whether a second session is needed (NHS).

After ureteroscopy, discharge is usually the same day or the following morning. The dominant experience is often the stent, a soft plastic tube left in the ureter to keep it open while swelling settles. Stents can cause a frequent urge to urinate, a dull ache in the flank or bladder, and blood in the urine, especially with activity. These symptoms are unpleasant but expected. The stent is removed in a brief clinic procedure, sometimes by pulling a string left attached to it; the timing is set by your surgeon and depends on how the ureter looked during the operation. The NIDDK notes that stents are typically placed to help urine drain and are removed after the ureter has had time to heal (NIDDK).

After PCNL, a hospital stay of a night or more is usual, and there may be a temporary drainage tube from the back. Returning to desk work often takes a week or two; heavier activity takes longer. Your team will give specific guidance.

Whatever the route, keep any follow-up appointment. It confirms the stone is truly gone, checks the kidney has recovered, and opens the more important conversation about why the stone formed and how to reduce the chance of the next one.

What people often get wrong about kidney stones and surgery

Kidney stone folklore is abundant, and some of it steers people toward harm. A few corrections, grounded in what the evidence actually shows.

“If it hurts this much, it must be huge.” Pain reflects spasm and pressure, not diameter. Some of the most excruciating episodes involve stones of 2 to 3 mm. Only imaging can tell you the size (Mayo Clinic).

“Drinking gallons of water will flush it out.” Adequate fluid keeps urine flowing and is genuinely helpful, but forcing extreme volumes does not push a stone that is too wide for the ureter, and it can make nausea worse. The NIDDK’s guidance is to drink enough to keep urine pale, not to drown the stone (NIDDK).

“Once the pain stops, the stone is gone.” Pain can fade because the ureter has stopped spasming around a stone that is still lodged, or because the kidney has become so distended that it stops signaling. Silence is not proof of passage; a follow-up scan is.

“Lithotripsy is always the gentlest option.” It avoids incisions, but it can require repeat sessions, fragments still have to pass, and it works poorly on very hard stones. For many ureteral stones, ureteroscopy clears the problem in one visit.

“Herbal remedies dissolve stones.” No mainstream guideline supports any supplement or herbal product for dissolving calcium stones, which make up the large majority. A specific type of stone made of uric acid can sometimes be shrunk by making the urine less acidic under medical supervision, but that is a prescribed strategy for a diagnosed stone type, not a general remedy (NIDDK).

“Small stones in the kidney should always come out.” Quiet, non-obstructing stones are often monitored, because the procedure carries more risk than the stone does.

Questions to ask your care team before deciding

A consultation about a stone moves fast, and the questions that matter most often surface on the drive home. Bring this list, or a version of it, and write the answers down.

• How big is my stone in millimeters, and exactly where is it: in the kidney, or in the upper, middle or lower ureter?
• Is the kidney behind it swollen, and does my blood work show that it is still functioning normally?
• Given that size and location, what is your honest sense of the chance it passes on its own, and over roughly what time frame?
• If we wait, what is the plan: when will you re-scan, and which symptoms should bring me straight back?
• Is a medicine to relax the ureter appropriate for me, and what side effects should I expect from it?
• If a procedure is needed, which one do you recommend for my stone and why? What would make you choose a different one?
• Will I have a stent? For how long, what will it feel like, and how is it removed?
• What are the realistic risks of the procedure you are suggesting, and what happens if fragments remain?
• How long before I can return to work, drive, exercise and travel?
• Can the stone be analyzed once it is out, and will you order the urine and blood tests that explain why it formed?
• What should I change, in diet or fluids, to make the next stone less likely?

Two habits help. Ask the team to point to your own scan while they explain; a stone becomes far less abstract when you see it. And if the recommendation is to wait, ask them to say out loud what would change their mind. That single answer turns a vague instruction into a plan you can follow with confidence.

When to call your doctor: red-flag signs with a kidney stone

Watchful waiting only works if you know when to stop waiting. The following signs mean you should contact your care team the same day or go to an emergency department, whether you are waiting for a stone to pass or recovering from a procedure. This list echoes guidance from the NHS, Mayo Clinic and MedlinePlus (NHS; Mayo Clinic; MedlinePlus).

• A fever, chills or shaking, or feeling suddenly unwell. Infection behind a blocked kidney can become life-threatening within hours and needs urgent drainage.
• Pain so severe that you cannot sit still or find a comfortable position, or pain that no longer responds to the relief you were given.
• Persistent vomiting, or being unable to keep any fluids down, which raises the risk of dehydration and makes passage less likely.
• Difficulty passing urine, passing very little, or none at all, especially if you have only one kidney.
• Urine that is heavily bloody, contains clots, or is cloudy and foul-smelling.
• Pain that has moved to both sides, or new confusion, drowsiness, or a rapid heartbeat.
• After a procedure: heavy bleeding, a stent that seems to have fallen out, worsening flank pain, or a temperature.

Less urgent but still worth a call: symptoms that have persisted beyond the time frame your team expected, a stone that has not appeared despite the pain settling, or new questions about your medicines. Keep the clinic number somewhere you can find it, and if you have been told to strain your urine, keep doing so until someone confirms the stone is out. When in doubt, call. Clinicians would far rather hear from you early than meet you in intensive care.

Frequently asked questions

How do you know if you need surgery for kidney stones?

You find out through imaging and blood tests, not from pain alone. A CT scan or ultrasound measures the stone, locates it, and shows whether the kidney is swollen; blood tests check kidney function and infection. Surgery is usually discussed when a stone is too large to pass, has stopped moving, blocks urine flow, or comes with fever, uncontrolled pain, or a single kidney. The urologist weighs all of this with you.

At what size do kidney stones typically require surgery?

The NHS describes stones of about 6 to 7 mm or larger as generally too big to pass naturally and the most likely to need a procedure. Smaller stones are usually given time to pass with fluids and pain relief. Size is a strong signal rather than a fixed rule, because a small stone with infection needs urgent care while a larger quiet stone in the kidney may simply be monitored.

Can kidney stones go away without surgery?

Yes, most do. The NHS notes that the majority of kidney stones are small enough to pass in the urine, typically within days to a few weeks, with pain managed at home. Drinking enough to keep urine pale, treating pain, and sometimes a medicine that relaxes the ureter all support passage. A follow-up scan confirms the stone is out; the absence of pain alone is not proof.

How long can a kidney stone be left untreated?

For a small stone with no fever, no infection and normal kidney function, a few weeks of supervised waiting is routine, with a re-scan to confirm progress. The risk is not the calendar itself but what the stone does meanwhile: a complete blockage can gradually injure the kidney, and any fever signals infection that needs urgent drainage. Quiet, non-blocking stones inside the kidney may be monitored for years.

Do kidney stones pass on their own more easily from certain locations?

Yes. Stones in the lower ureter, near the bladder, have already passed two of the tube’s three natural narrowings and often clear quickly. Stones in the upper ureter, close to the kidney, have all three ahead of them and are more likely to stall. Stones resting inside the kidney itself are not moving at all and are usually watched unless they grow, bleed, or cause infections.

What are the signs you need kidney stone surgery urgently rather than waiting?

Fever or chills with a known stone, pain that cannot be controlled, persistent vomiting, passing very little or no urine, and heavily bloody or foul-smelling urine all mean same-day medical attention. People with a single kidney or reduced kidney function are also treated earlier. These signs suggest infection or a dangerous blockage, and guidelines treat infection behind an obstruction as an emergency requiring prompt drainage.

Is kidney stone surgery a major operation?

Usually not in the traditional sense. Shock wave lithotripsy uses external sound waves with no incision, and ureteroscopy passes a thin scope through the urethra, also without a cut; both are often same-day procedures. Percutaneous nephrolithotomy, used for large kidney stones, involves a small incision in the back and a short hospital stay. All require anesthesia and carry procedure-specific risks your surgeon will explain.

Why do I need a stent after ureteroscopy, and what does it feel like?

A stent is a soft tube that keeps the ureter open while swelling from the procedure settles, allowing urine to drain freely. It commonly causes urinary urgency, a dull flank or bladder ache, and some blood in the urine, particularly with activity. These effects are expected and temporary. Your surgeon decides how long it stays based on how the ureter looked, and removal is a brief clinic procedure.

Can medicine dissolve a kidney stone instead of surgery?

Only for one uncommon stone type. Stones made of uric acid can sometimes be shrunk by making the urine less acidic under medical supervision, according to the NIDDK. Calcium-based stones, which make up the large majority, cannot be dissolved by any medicine or supplement. Alpha blockers do not dissolve stones; they relax the ureter to help a stone pass. No herbal product is supported by mainstream guidelines.

Will the stone come back after it passes or is removed?

It can. Having had one stone raises the likelihood of another, which is why the follow-up conversation matters as much as the procedure. Analyzing the stone, checking blood and urine chemistry, and adjusting fluid intake and diet based on the results are the standard steps described by the NIDDK and Mayo Clinic. Your team can tailor prevention to the type of stone you formed.

References

• NHS: Kidney stones, Treatment
• NIH NIDDK: Treatment for Kidney Stones
• MedlinePlus: Kidney Stones
• Cleveland Clinic: Kidney Stones

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.