What size of kidney stone passes?
If your report says "8 mm", see what that means with a familiar comparison from the kitchen. Move the slider to explore the chance of passing the stone by size and the treatments usually considered.
The chance of a stone passing depends not only on its size but also on its location (kidney/ureter), its composition and the anatomy of the urinary tract. Fever, persistent pain or inability to urinate are emergencies.
Lentil ≈ 2–4 mm
Small stone. Most ureteral stones under 5 mm pass on their own with plenty of fluids and pain control, usually within a few weeks.
Chickpea ≈ 5–9 mm
The chance of passing on its own decreases. Medication to help the stone pass may be tried; if it does not pass, or if there is pain, infection or kidney swelling, it is broken up with a laser by ureteroscopy (URS).
Kidney stone treatmentsHazelnut ≈ 10–20 mm
Usually does not pass on its own. In the kidney, minimally invasive laser surgery with flexible ureteroscopy (RIRS) or shock wave lithotripsy (ESWL); in the ureter, URS is often preferred.
Minimally invasive laser stone surgeryOlive > 20 mm
Large stone. For kidney stones over 2 cm, percutaneous nephrolithotomy (PCNL) is usually the first option; RIRS may be used in selected patients.
Kidney stone treatmentsMost stones under 5 mm pass on their own. For stones between 5–10 mm, the chance of passing decreases and medication may be tried. Stones larger than 1 cm usually do not pass on their own; they are treated with minimally invasive laser methods (URS, RIRS) or, for large stones, with PCNL.
Why does stone size matter?
When a stone formed in the kidney moves into the urinary channel (ureter), it can block it and cause severe flank pain (renal colic). A stone's chance of passing on its own depends mostly on its size; however, its location, shape and the structure of the urinary tract also play a role.
Treatment by stone size
| Size | Comparison | Usually considered |
|---|---|---|
| Under 5 mm | Lentil | Plenty of fluids, pain control, monitoring |
| 5–10 mm | Chickpea | Medication to help the stone pass; URS (laser) if it does not pass |
| 10–20 mm | Hazelnut | RIRS or ESWL in the kidney, URS in the ureter |
| Over 20 mm | Olive | PCNL (RIRS in selected patients) |
When should you seek urgent care?
Pain accompanied by fever and chills, pain that does not ease despite painkillers, inability to urinate, or a suspected stone in someone with a single kidney requires urgent evaluation. A blocked kidney with infection can be damaged quickly.
Preventing stone formation
Drinking enough fluid to keep daily urine output above 2–2.5 liters, reducing salt and balancing animal protein lower the risk of stones. For recurrent stones, stone analysis and a metabolic evaluation are recommended. For details on stone treatment, you can visit the kidney stone diseases page.
Frequently asked questions
What size of kidney stone passes on its own?
Will an 8 mm stone pass?
What is the difference between RIRS and URS?
What does it feel like when a kidney stone is passing?
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