What Size Kidney Stone Can Pass on Its Own?
If you have been told you have a kidney stone, one of the first questions is usually: “Will this pass by itself?”
The short answer is that stones under 5 mm have a relatively high chance of passing naturally once they are in the ureter. Stones between 5 and 10 mm may still pass, but the likelihood generally falls as the stone becomes larger. Stones over 10 mm are much less likely to pass without treatment.[1,3,4]
However, size is only part of the story.
Kidney Stone Size and Chance of Passing
Published studies and European urological guidelines show a clear relationship between stone size and spontaneous passage.[1,3,4]
As a practical guide:
Under 5 mm: often passes naturally.
5–7 mm: may pass, but less reliably.
7–10 mm: increasingly unlikely to pass without treatment.
Over 10 mm: usually has a low likelihood of spontaneous passage.
The EAU guidelines report spontaneous passage in approximately 75% of ureteric stones smaller than 5 mm. If a stone under 5 mm has already reached the lower ureter near the bladder, the reported passage rate is approximately 89%.[1]
Another CT-based study found passage rates of approximately:
76% for stones measuring 2–4 mm
60% for stones measuring 5–7 mm
48% for stones measuring 7–9 mm
25% for stones larger than 9 mm.[3]
These numbers are useful estimates rather than guarantees for an individual patient.
Location Matters Almost as Much as Size
A stone sitting inside the kidney is different from a stone that has entered the ureter.
When discussing whether a stone will “pass”, doctors are usually referring to a ureteric stone travelling from the kidney toward the bladder.
Stones closer to the bladder generally have a better chance of passing than stones high in the ureter.[1,3]
For example, a 5 mm stone close to the bladder may behave very differently from a 5 mm stone near the kidney.
How Long Should a Kidney Stone Take to Pass?
The EAU reports an average spontaneous passage time of around 17 days, although the range is wide.[1]
Observation may be appropriate when:
pain can be controlled;
there is no significant infection;
kidney function is satisfactory;
there is no concerning ongoing obstruction; and
the stone has a reasonable chance of passing.
Medical expulsive therapy may also be considered in selected patients after clinical assessment.[1]
Importantly, pain stopping does not always prove that the stone has passed. Follow-up imaging may sometimes be recommended.
When Should You Seek Urgent Treatment?
A stone does not have to be large to become dangerous.
Seek urgent medical assessment if kidney stone symptoms occur with:
fever or chills;
feeling significantly unwell;
uncontrolled pain;
persistent vomiting;
difficulty or inability to pass urine; or
known obstruction with infection.
An infected and obstructed kidney can require emergency drainage rather than waiting for the stone to pass.
When Does a Kidney Stone Need Surgery?
There is no single stone size that automatically means surgery is required.
Treatment is based on the combination of stone size, location, symptoms, obstruction, infection, kidney function, anatomy and individual circumstances.[1,2]
If a stone is unlikely to pass or continues to cause problems, options may include ureteroscopy and laser stone treatment or other stone procedures depending on the situation.
You can read more about when a kidney stone may need surgery.
Have You Already Had a CT Scan?
The most useful question is not simply “How many millimetres is my stone?” but where is it, is it obstructing the kidney, and how likely is it to pass safely?
If you already have CT imaging, it can be reviewed as part of a kidney stone assessment to determine whether observation or treatment may be appropriate.
Patients from Brisbane, regional or interstate Australia, and overseas can have existing imaging and investigations reviewed when planning the appropriate pathway.
For people who develop stones repeatedly, further assessment may also include kidney stone prevention and 24-hour urine testing.
Medical Disclaimer
This information is general educational information and does not replace personalised medical advice. Kidney stone treatment depends on stone size and location, symptoms, infection, urinary obstruction, kidney function, medical history and individual circumstances. Seek urgent medical attention for fever, chills or significant illness associated with suspected urinary obstruction.
References
Skolarikos A, Geraghty R, Somani B, et al. European Association of Urology Guidelines on the Diagnosis and Treatment of Urolithiasis. Eur Urol. 2025;88(1):64-75. doi:10.1016/j.eururo.2025.03.011.
Pearle MS, Matlaga BR, Antonelli JA, et al. Surgical Management of Kidney and Ureteral Stones: AUA Guideline (2026) Part I: Evaluation and Treatment of Patients With Kidney and/or Ureteral Stones. J Urol. 2026;215(2):113-123. doi:10.1097/JU.0000000000004842.
Coll DM, Varanelli MJ, Smith RC. Relationship of spontaneous passage of ureteral calculi to stone size and location as revealed by unenhanced helical CT. AJR Am J Roentgenol. 2002;178(1):101-103. doi:10.2214/ajr.178.1.1780101.
Jendeberg J, Geijer H, Alshamari M, Cierzniak B, Lidén M. Size matters: the width and location of a ureteral stone accurately predict the chance of spontaneous passage. Eur Radiol. 2017;27(11):4775-4785. doi:10.1007/s00330-017-4852-6.
