Urology

STONE Nephrolithometry Score for Renal Calculi calculator

Enter the published formula inputs below to calculate and interpret this score.

Clinical inputs

Stone size (area)

mm²

Allowed range: 1–20000 mm²

Stone area on noncontrast CT in square millimetres. Under 400 scores 1, 400 to 799 scores 2, 800 to 1599 scores 3, 1600 or more scores 4.

Tract length (skin to stone)

Allowed range: 10–300 mm

100 mm or less scores 1. Over 100 mm scores 2.

Obstruction (hydronephrosis)

Number of involved calyces

Essence (stone density)

Allowed range: 0–3000 HU

Mean stone density in Hounsfield units. 950 or less scores 1. Over 950 scores 2.

Result

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Primary source

Okhunov Z, Friedlander JI, George AK, Duty BD, Moreira DM, Srinivasan AK, Hillelsohn J, Smith AD, Okeke Z. S.T.O.N.E. nephrolithometry: novel surgical classification system for kidney calculi. Urology. 2013;81(6):1154-1159. DOI: 10.1016/j.urology.2012.10.083. PMID: 23540858. Five noncontrast CT features are scored. Stone size (area): under 400 mm² 1, 400-799 mm² 2, 800-1599 mm² 3, 1600 mm² or more 4. Tract length (skin to stone): 100 mm or less 1, over 100 mm 2. Obstruction: no or mild hydronephrosis 1, moderate or severe hydronephrosis 2. Number of involved calyces: 1-2 calyces 1, 3 calyces 2, complete staghorn 3. Essence (stone density): 950 HU or less 1, over 950 HU 2. The total is 5 to 13. The original table is paywalled; points and the 950 HU boundary (950 or less scores 1, over 950 scores 2) follow Table 1 'as described by Okhunov et al.' in Ihedoro IE et al., Cureus 2025;17(8):e90570 (PMID 40978999), which agrees with Wei B et al., Sci Prog 2025;108(4) (PMID 41217967) and Choudhary A et al., Rev Mex Urol 2023;83(3). Hoa TQ et al., Med Arch 2024 (PMID 38481581) prints the boundary the other way (under 950 scores 1, 950 or more scores 2) and is not followed. In the derivation cohort of 117 patients, stone-free patients had a lower mean score than those with residual stones (6.8 vs 9.7); the abstract prints no complexity cutoffs. (2013)

Scope: Adults with kidney stones planned for percutaneous nephrolithotomy, scored from noncontrast CT. Higher totals mean more complex stones; it is not for ureteral stones and gives no fixed risk categories.

Last reviewed 2026-10-18

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Professional use only

For qualified clinicians. Independently verify inputs, calculations, source guidance, and applicability before any clinical action. This calculator does not replace clinical judgment.

Source: Okhunov Z, Friedlander JI, George AK, Duty BD, Moreira DM, Srinivasan AK, Hillelsohn J, Smith AD, Okeke Z. S.T.O.N.E. nephrolithometry: novel surgical classification system for kidney calculi. Urology. 2013;81(6):1154-1159. DOI: 10.1016/j.urology.2012.10.083. PMID: 23540858. Five noncontrast CT features are scored. Stone size (area): under 400 mm² 1, 400-799 mm² 2, 800-1599 mm² 3, 1600 mm² or more 4. Tract length (skin to stone): 100 mm or less 1, over 100 mm 2. Obstruction: no or mild hydronephrosis 1, moderate or severe hydronephrosis 2. Number of involved calyces: 1-2 calyces 1, 3 calyces 2, complete staghorn 3. Essence (stone density): 950 HU or less 1, over 950 HU 2. The total is 5 to 13. The original table is paywalled; points and the 950 HU boundary (950 or less scores 1, over 950 scores 2) follow Table 1 'as described by Okhunov et al.' in Ihedoro IE et al., Cureus 2025;17(8):e90570 (PMID 40978999), which agrees with Wei B et al., Sci Prog 2025;108(4) (PMID 41217967) and Choudhary A et al., Rev Mex Urol 2023;83(3). Hoa TQ et al., Med Arch 2024 (PMID 38481581) prints the boundary the other way (under 950 scores 1, 950 or more scores 2) and is not followed. In the derivation cohort of 117 patients, stone-free patients had a lower mean score than those with residual stones (6.8 vs 9.7); the abstract prints no complexity cutoffs. (2013)

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Clinical inputs

Stone size (area) (mm²)Accepted range: 1 to 20000
Tract length (skin to stone) (mm)Accepted range: 10 to 300
Obstruction (hydronephrosis)
Number of involved calyces
Essence (stone density) (HU)Accepted range: 0 to 3000

Primary source

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