How this calculator works
Select categories assigned by a clinician from preoperative non-contrast CT. S.T.O.N.E. refers to stone size, tract length, obstruction, number of involved calyces and essence (attenuation). It was developed for percutaneous nephrolithotomy, not for deciding whether acute flank pain is due to a stone. The total describes operative complexity; this page does not convert it into an individual success probability. The result is an estimate for information only and is not medical advice.
Formula
Total = size points (1-4) + tract points (1-2) + obstruction points (1-2) + calyx points (1-3) + attenuation points (1-2). The possible range is 5 to 13. Stone size is an area in mm², not a linear diameter.
Worked example
The lowest category for each factor gives 1 + 1 + 1 + 1 + 1 = 5. A large stone with a long tract, substantial hydronephrosis, complete staghorn involvement and high attenuation gives 4 + 2 + 2 + 3 + 2 = 13.
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Frequently asked questions
Is this the emergency-department STONE score?
No. It is S.T.O.N.E. nephrolithometry for PCNL planning, a separate instrument from the acute renal-colic prediction rule.
Can I enter a stone diameter as its size?
No. The size categories use assessed stone area in square millimetres.
Does the total predict a complication with certainty?
No. Outcome relationships vary by population and surgical technique; specialist judgement remains necessary.