A kidney stone size chart can help you understand a scan report, but size alone cannot tell you whether a stone will pass or which treatment you need.
Doctors also consider the stone’s location, whether it blocks urine flow, your symptoms, and your kidney function. A small stone causing complications may need treatment sooner than a larger stone found incidentally.
Seek urgent medical assessment for fever or chills, inability to urinate, uncontrolled pain, or persistent vomiting. Do not assume these symptoms are safe because your stone is small.
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For optional reading alongside medical advice, view the Kidney Stone Removal Report. It is an information product, not a way to determine whether your stone can safely pass without treatment.
Kidney Stone Size Chart
The chart below provides general guidance for adults. The passage information primarily concerns stones in the ureter, the tube connecting the kidney to the bladder.
| Stone size | Measurement in centimeters | What the size may mean |
|---|---|---|
| Under 5 mm | Under 0.5 cm | Smaller ureteral stones are more likely to pass. Observation may be appropriate when there are no complications. |
| 5–9 mm | 0.5–0.9 cm | Passage remains possible, but becomes less likely as size increases. Location and follow-up findings help determine whether to wait or intervene. |
| 10 mm | 1 cm | A size at which active treatment is often discussed, particularly for a ureteral stone. It does not automatically mean emergency surgery. |
| Over 10–20 mm | Over 1–2 cm | Procedures are commonly considered. For stones in the kidney, options may include ureteroscopy or shock-wave treatment. |
| Over 20 mm | Over 2 cm | Large kidney stones generally require specialist treatment. Percutaneous nephrolithotomy, or PCNL, is usually the first-line procedure. |
These are broad decision ranges, not guaranteed outcomes or instructions to wait at home. Treatment recommendations also differ between kidney stones and ureteral stones.
How to Read Your Stone Measurement
Millimeters and Centimeters
Kidney stone measurements are commonly written in millimeters, abbreviated mm.
To convert centimeters to millimeters, multiply by 10:
- 0.4 cm = 4 mm
- 0.6 cm = 6 mm
- 0.8 cm = 8 mm
- 1.2 cm = 12 mm
- 2.5 cm = 25 mm
A report describing a 0.6 cm stone therefore means the same size as a 6 mm stone.
What Does “6 × 4 mm” Mean?
This describes two dimensions of the same stone. It does not mean that you have a 10 mm stone.
Similarly, “two 4 mm stones” means two separate stones, not one 8 mm stone. Your clinician may consider their combined burden when planning treatment, but the individual measurements still matter.
Ask the clinician to explain which measurement they are using when discussing passage or treatment.
Read More Than the Number
Imaging helps establish where stones are and whether there is a blockage. Your assessment may also include urine and blood tests; a size measurement does not replace those findings.
When reviewing your report, ask:
- Which kidney or ureter contains the stone?
- Is there one stone or more than one?
- Is urine draining normally?
- Is there evidence of infection?
- What follow-up is needed?
Why Stone Location Matters
A Stone Still Inside the Kidney
A stone resting inside the kidney is different from one already moving through the ureter.
Some non-obstructing kidney stones without symptoms can be monitored. They do not necessarily begin passing as soon as they are discovered.
A Stone in the Ureter
A stone nearer the bladder generally has a greater chance of passing than a similar-sized stone higher in the ureter.
That is why a measurement such as “5 mm” needs a location alongside it before it becomes useful for treatment decisions.
For a separate explanation of timing, read how long it takes to pass a kidney stone.
Does a Larger Stone Always Cause More Pain?
Pain is not a reliable ruler for measuring a stone.
A stone moving into the ureter can cause severe colic. Symptoms may fluctuate, so the amount of discomfort does not reliably tell you the stone’s size or prove that it has passed.
Avoid making decisions such as:
- “It barely hurts, so it must be small.”
- “The pain is severe, so the stone must be large.”
- “The pain stopped, so I no longer need follow-up.”
Use the scan findings and your clinician’s assessment to guide the next step.
What Treatment Might Be Recommended?
Observation With Follow-Up
For a suitable stone, your clinician may recommend waiting for passage while managing symptoms.
Ask for a review date, instructions for collecting the stone, and a clear explanation of when to return earlier. Observation should be an agreed care plan with follow-up.
Medicines
Pain relief and anti-sickness medicines may help manage an episode. A clinician may also consider an alpha blocker for selected ureteral stones. This does not guarantee passage or make every stone suitable for observation.
Shock-Wave Lithotripsy
Shock waves delivered from outside the body break a stone into smaller pieces that can pass through the urinary tract.
Ureteroscopy
A thin instrument passes through the urinary tract to reach the stone. The clinician can remove it or break it into smaller fragments.
Percutaneous Nephrolithotomy
PCNL accesses the kidney through a small incision in the back to remove or fragment a stone. It is commonly used for larger stones.
Read our kidney stone treatment options guide for more detail about these approaches.
If you explore the Kidney Stone Removal Report, discuss any suggested approach with your clinician. Do not use a home-remedy schedule to delay recommended treatment.
When Size Becomes Secondary
An infected, obstructed urinary system is an emergency. Urgent drainage and antibiotics may be needed before the stone itself is treated.
Persistent obstruction, uncontrolled pain, or worsening kidney function can also make continued observation inappropriate.
Get urgent help if you develop:
- Fever or shaking chills.
- Inability to urinate, or only a very small amount.
- Severe pain that prescribed treatment does not control.
- Repeated vomiting or inability to keep fluids down.
Tell the treating team promptly if you have one functioning kidney. This changes the urgency of assessment.
Questions to Ask at Your Appointment
Bring your scan report and medication list. Useful questions include:
- What is the stone’s size and exact location?
- Is it blocking urine flow or affecting kidney function?
- Is observation reasonable in my situation?
- Would medicine help, and what are its limitations?
- If I need a procedure, why do you recommend that option?
- When should I return for review?
- How will we confirm that the stone has passed or been cleared?
These questions turn a measurement into a practical plan.
Frequently Asked Questions
Is a 4 mm kidney stone small?
Yes, it falls within the under-5-mm range. However, “small” does not establish whether it is safe to wait. Its location and any complications still need assessment.
Can a 6 mm or 7 mm stone pass naturally?
Some can, particularly when already near the bladder. Passage is not guaranteed, and the decision to observe requires follow-up.
Does a 10 mm stone always require surgery?
No single measurement determines every case. A 10 mm stone warrants a treatment discussion, and its location helps determine which options are appropriate.
Does passing one stone mean all my stones are gone?
Not necessarily. If your scan showed multiple stones, ask which ones remain and how they will be monitored. Follow the collection instructions if you pass a stone so it can be analyzed.
Can I cancel follow-up when the pain stops?
Contact your care team first. Follow-up is intended to establish whether the stone has passed, not simply whether the pain has improved.
What should I do after the stone is cleared?
Ask about stone analysis and a prevention plan. Our recurrent kidney stone guide explains topics to discuss after repeated episodes.
Optional further reading: Kidney Stone Removal Report. Purchasing an information product is not necessary to receive appropriate treatment or prevention advice.
Resources
- European Association of Urology: Urolithiasis Guidelines
- NICE: Renal and Ureteric Stones—Assessment and Management
- NIDDK: Treatment for Kidney Stones
- NIDDK: Diagnosis of Kidney Stones
- NHS: Kidney Stones
- Cambridge University Hospitals: Information for Patients With Renal/Ureteric Colic
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Medical disclaimer: This article provides general information and does not replace personalized medical advice, diagnosis, or treatment. A size chart cannot determine whether observation is safe for your individual stone.