Kidney Stone Size: Which Stones Pass on Their Own and Which Need Laser Treatment
Updated: 1 day ago
Most kidney stones up to 4 mm pass on their own. In addition, around 68 in 100 stones up to 5 mm pass too. Between 5 and 10 mm, the chance drops to roughly half, and above 10 mm most stones need laser, shock wave or keyhole treatment.
Medically reviewed by Assoc. Prof. Dr. Tuncay Taş, urologist. Updated November 2026.
However, size is only one part of the answer. Location, shape, density, infection and your pain level also shape the plan. This guide explains each factor, so the number on your scan report makes sense.
Kidney stone size chart in millimetres
The chart below gives the usual picture for a single stone in an adult. Still, these are averages, so your own scan and symptoms always come first.
Stone size | Rough comparison | Chance of passing | Usual plan |
Up to 2 mm | A grain of sand | Very high | Fluids, pain relief, strain urine |
3 to 4 mm | A grain of rice, end on | High, most pass | Watchful waiting, often with a tablet to relax the ureter |
5 mm | A pencil eraser | About 68 in 100 (5 mm and under) | Watchful waiting for up to 4 to 6 weeks |
6 to 7 mm | A peppercorn | About 47 in 100 (5 to 10 mm) | Short trial of passage, low threshold for treatment |
8 to 10 mm | A pea | Low | Laser ureteroscopy or shock wave treatment in most cases |
10 to 20 mm | A coin edge to a US penny | Very low | Laser RIRS or shock wave treatment |
Over 20 mm | Larger than a US penny | Does not pass | Mini PCNL through a small tunnel in the back |
The passing rates come from pooled studies of ureter stones. In fact, many real stones fall between rows.
For example, a 5.5 mm stone near the bladder may pass. Meanwhile, a 4.5 mm stone stuck higher up may not.
How big is a 4, 5, 6 or 7 mm kidney stone?
The ureter is the tube that carries urine from the kidney to the bladder. Inside, it measures only about 3 to 4 mm across.
So even a 4 mm stone stretches it. That stretch causes the classic wave-like pain.
4 mm and under
These stones are small, and most pass within days to a few weeks. Even so, small does not always mean painless. In particular, a 3 mm stone can hurt as much as a large one.
5 to 6 mm
This is the grey zone. About two in three stones up to 5 mm pass.
However, the odds fall with every extra millimetre. Therefore, a urologist usually sets a time limit for waiting, often 4 to 6 weeks.
7 mm and above
A 7 mm stone can still pass, especially when it sits close to the bladder. However, many men and women with stones of this size end up needing treatment. Above 10 mm, waiting rarely works.
Why location matters as much as size
Where the stone sits changes the plan as much as how big it is. For this reason, scan reports name the site as well as the size.
Lower ureter, near the bladder: the best chance of passing, because the stone has the shortest way to go.
Upper ureter, near the kidney: a lower chance of passing, and pain often lasts longer.
Inside the kidney: a stone that does not move may cause no symptoms at all. Small, silent kidney stones are often just watched.
Lower part of the kidney: fragments clear less easily after shock waves, so laser RIRS is often the better choice there.
A pouch off the kidney (calyceal diverticulum): stones here cannot drain out and usually need a laser.
Dr. Taş has published on several of these questions. For example, his team studied laser RIRS for stones hidden in a calyceal diverticulum. They also tested patient position during shock waves for lower kidney stones.
Other factors that change the decision
Two stones of the same size can need different care. Beyond size and site, a urologist looks at the following points.
Stone density
CT measures stone hardness in Hounsfield units. Hard stones break poorly with shock waves.
In fact, Dr. Taş and colleagues linked higher density to lower shock wave success in ureter stones. Later, a second study looked at density and laser RIRS results.
Infection and kidney function
A stone that blocks an infected kidney is dangerous at any size. Likewise, a stone in a single working kidney needs quicker action. In both cases, size charts do not apply.
Pain, work and travel
Some people cannot wait weeks with pain. Pilots, long-haul drivers and frequent travellers often choose early treatment too.
In the UK, NICE advises treatment within 48 hours for severe ongoing pain. The same applies when the stone is unlikely to pass.
The silent risk of waiting too long
A blocked kidney can lose function quietly, even when pain settles. Dr. Taş also reported a rare case of a ruptured kidney drainage system during watchful waiting. Therefore, waiting should always include a time limit and a follow-up scan.
Stone type: the factor most charts leave out
Stones differ in what they are made of, and that changes the plan. Therefore, a lab test of a passed or removed stone is worth the effort.
Calcium oxalate: the most common type. These stones are often hard, so larger ones respond better to a laser than to shock waves.
Uric acid: these can sometimes dissolve with tablets that make urine less acidic. As a result, some people avoid a procedure altogether.
Struvite: these form with certain urine infections. They can grow fast and fill the kidney as a staghorn stone, so full removal matters.
Cystine: a rare inherited type. They tend to come back, so long-term prevention is part of the plan.
A CT scan gives a first clue to the type. For example, uric acid stones usually show a lower density than calcium stones. Even so, only a lab test of the stone itself confirms it.
Silent kidney stones: can a large stone stay?
Many stones turn up by chance on a scan for something else. In that case, the question changes from "will it pass?" to "should it come out?".
NICE suggests watchful waiting for silent kidney stones under 5 mm. For larger silent stones, waiting is also an option after an honest talk about the risks. Those risks include sudden pain, infection and slow growth.
In practice, several points favour early removal:
Growth: a stone that grows between scans tends to keep growing.
Travel and work: pilots and people who travel to remote places often need to be stone-free.
Infection: repeated urine infections suggest the stone holds bacteria.
Single kidney: a blockage would affect all kidney function.
Otherwise, a yearly scan is usually enough for a small, silent stone. Meanwhile, the prevention steps below lower the chance of growth.
How long does it take to pass a kidney stone?
Most stones that will pass do so within 2 to 4 weeks. Smaller stones usually pass sooner, often within 1 to 2 weeks.
After about 4 to 6 weeks, however, the chance of passing falls. Meanwhile, the risk to the kidney rises.
Meanwhile, these steps can help:
Drink enough: aim for pale urine, unless your doctor limits fluids.
Use pain relief: NICE advises anti-inflammatory painkillers (NSAIDs) as the first choice, if they are safe for you.
Ask about tamsulosin: this tablet relaxes the lower ureter. NICE suggests considering it for stones under 10 mm low in the ureter.
Strain your urine: catch the stone so a lab can test what it is made of.
Keep moving: normal activity is fine, although it does not speed passage much.
Treatment options by stone size
When a stone will not pass, the size and site guide the choice of procedure. The table follows the NICE guideline NG118 for adults. In addition, it adds what each option means for you.
Stone and size | Usual options | What it involves |
Kidney stone under 10 mm | Shock wave lithotripsy (SWL); laser RIRS if SWL is unsuitable or fails | SWL works from outside the body; RIRS uses a thin scope with no cut |
Kidney stone 10 to 20 mm | Laser RIRS or SWL; PCNL if these fail | RIRS often clears the stone in one session |
Kidney stone over 20 mm, including staghorn | PCNL; laser RIRS if PCNL is not an option | A tunnel under 1 cm wide in the back, 1 to 2 nights in hospital |
Ureter stone under 10 mm | SWL or laser ureteroscopy | Ureteroscopy is usually a day case or 1 night |
Ureter stone 10 to 20 mm | Laser ureteroscopy | The scope reaches the stone and a laser breaks it up |
Shock wave lithotripsy
Shock waves pass through the skin and crack the stone. You need no general anaesthetic.
However, it works best for softer stones under about 10 mm. Also, the fragments still have to pass.
Laser ureteroscopy and RIRS
A thin scope enters through the urethra and bladder, so there is no wound. Then a laser breaks the stone into dust or small pieces. For most kidney stones under 2 cm, laser RIRS clears the stone in one session.
Mini PCNL
For stones over 2 cm, the surgeon makes a small tunnel from the back into the kidney. As a result, large stones come out in one operation. Recovery takes a little longer than after RIRS.
For recovery, stents and travel, see the kidney stone surgery page.
Fragments, stents and flying after treatment
After laser or shock wave treatment, small fragments often remain. Most of them pass over the next few weeks. However, fragments over about 4 mm can grow into a new stone, so a follow-up scan checks the result.
A stent is a soft tube from the kidney to the bladder. It keeps urine flowing while swelling settles, and it usually stays for 1 to 2 weeks. Meanwhile, it can cause an urge to pass urine and some blood in the urine, which is common and settles after removal.
For travellers from the US, Canada or the UK, timing matters too. In general, you can fly once you pass urine normally, have no fever and your pain is under control. In addition, a discharge letter should state when any stent must come out, so a local urologist can remove it on time.
How doctors measure stone size
The size on your report depends on the scan. A low-dose CT scan without contrast is the most accurate test. NICE also recommends it for suspected kidney colic in adults.
CT: gives size, site and density. Even so, different settings can change the reading by 1 or 2 mm.
Ultrasound: avoids radiation, but it often overestimates size and can miss stones in the ureter.
Plain X-ray: useful for follow-up of stones that show up on X-ray, though some stones are invisible on it.
Reports usually give the largest dimension. Nevertheless, a long, thin stone may pass more easily than a round one. So ask for all three measurements if your report gives only one.
When a kidney stone is an emergency
Most stone pain is severe but not dangerous. Some signs, however, mean the kidney is at risk. Seek urgent care at once if you notice any of these:
Fever of 38°C (100.4°F) or higher, chills or shaking with stone pain.
Pain that painkillers do not control.
Repeated vomiting, so you cannot keep fluids down.
Passing very little or no urine.
A stone in your only working kidney, or stones in both sides.
A blocked, infected kidney needs drainage with a stent or a small tube, plus antibiotics. In that case, call 911 in the US or Canada. In the UK, call 999 or go to A&E.
Finally, keep a simple record of each stone: the date, the size, the side and what treatment you needed. This history helps any urologist in the US, Canada, the UK or Istanbul plan the next step quickly.
After the stone: lowering the chance of another
About half of people with one stone form another within years. Therefore, prevention matters as much as removal.
Stone analysis: knowing the stone type guides diet and medicine.
Fluids: enough to pass about 2 to 2.5 litres of urine a day, unless your doctor says otherwise.
Salt and protein: cut back on salty foods and large portions of meat.
Calcium: keep normal dietary calcium; very low calcium can raise oxalate stone risk.
Repeat stones: a 24-hour urine test helps find the cause.
When to see a urologist
See a urologist if your stone is over 5 mm or has not passed after 4 weeks. Also, ask for a review if pain keeps coming back. Similarly, repeated stones, a single kidney or a job where sudden pain is risky all justify a visit.
Assoc. Prof. Taş has over 20 years of experience in stone surgery. His work includes laser RIRS, ureteroscopy and mini PCNL.
To plan a visit, book a consultation or message the team on WhatsApp. Patients from the US, Canada and the UK receive a personal plan after the consultation.
Bring your scan images and the written report to the visit. Then size, site and density can be reviewed together with your symptoms and blood tests. As a result, the plan fits your stone, not an average from a chart.
Frequently asked questions
What size kidney stone can pass on its own?
Most stones up to 4 mm pass without treatment. Around 68 in 100 ureter stones up to 5 mm pass too. Between 5 and 10 mm, about 47 in 100 pass, while stones over 10 mm rarely do.
What size kidney stone needs surgery?
Size alone rarely decides. Stones over 10 mm usually need treatment, and stuck stones of 6 to 10 mm often do. However, fever, a blocked kidney or uncontrolled pain need treatment at any size.
How long does it take to pass a 5 mm kidney stone?
Most stones that pass do so within 2 to 4 weeks. Smaller stones often pass sooner. If a 5 mm stone has not moved after 4 to 6 weeks, a urologist usually discusses removal.
Is a 7 mm kidney stone big?
Yes, 7 mm is a medium stone. It can still pass, especially low in the ureter. However, many people with a 7 mm stone end up having laser or shock wave treatment.
Does stone location matter more than size?
Location matters as much as size. A stone close to the bladder passes more often than the same stone higher up. By contrast, a silent stone in the kidney may need no treatment at all.
Can a CT scan overestimate kidney stone size?
Yes, slightly, because scan settings can change the size by 1 or 2 mm. Ultrasound often makes stones look larger. So a low-dose CT without contrast gives the most reliable size.
When is a kidney stone an emergency?
A stone with fever or chills is an emergency, since it can mean an infected, blocked kidney. Uncontrolled pain, repeated vomiting or no urine also need urgent care. Call 911 in the US or Canada, or 999 in the UK.
Sources
About the reviewer
Assoc. Prof. Dr. Tuncay Taş is a urologist in Istanbul with more than 20 years of experience and patients from over 60 countries. He graduated from Istanbul University in 2004, trained at Taksim Training and Research Hospital, completed a uro-oncology and laparoscopy fellowship at Heidelberg University and belongs to the EAU and the Endourological Society. Read his full profile.
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