Calculators · Dermatology · Formula
Psoriasis BSA (hand/palm method)
Also called body surface area psoriasis, palm method, rule of palm
Estimates % body surface area involved by counting the patient's hand-sized (≈1%) and palm-sized (≈0.5%) areas.
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Formula and scoring
BSA% ≈ (number of patient's whole hands × 1) + (palm-only areas × 0.5). Meta-analysis: whole hand ≈ 0.87% in adults (13% below 1%); palm alone ≈ 0.5%.
Exam and ward pearls
- Use the patient's hand, not the examiner's.
- Rule of tens (Finlay): BSA >10% or PASI >10 or DLQI >10 = severe psoriasis.
When not to rely on it
- The 1% hand convention overestimates BSA in adults (especially women and high BMI) and underestimates it in children (Rhodes 2013).
Source
- Rhodes J, Clay C, Phillips M. The surface area of the hand and the palm for estimating percentage of total body surface area: results of a meta-analysis. Br J Dermatol. 2013;169(1):76-84. doi:10.1111/bjd.12290 · PMID 23448271
- Mrowietz U, Kragballe K, Reich K, et al. Definition of treatment goals for moderate to severe psoriasis: a European consensus. Arch Dermatol Res. 2011;303(1):1-10. doi:10.1007/s00403-010-1080-1 · PMID 20857129
- Finlay AY. Current severe psoriasis and the rule of tens. Br J Dermatol. 2005;152(5):861-7. doi:10.1111/j.1365-2133.2005.06502.x · PMID 15888138
Formula and cut-offs checked against these sources on 8 Nov 2026. Educational tool for clinicians; it does not replace clinical judgement.