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Body Surface Area (BSA)

BSA: Essential for dosing of dermatological therapeutics and quantitative assessment.

Body Weight

Body Height

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Enter height and weight to determine the body surface area using Mosteller and DuBois formulas.

Guidelines & Evidence

Verified

Last Review: 2026

When to Use

BSA estimation quantifies the percentage of total body surface area affected by a dermatological condition. It is a core component of disease severity assessment in psoriasis, atopic dermatitis, and other inflammatory skin diseases — used to classify mild vs. moderate-severe disease, determine eligibility for systemic or biologic therapy, and monitor treatment response.

Primary Clinical Uses

Psoriasis severity classification (mild < 3%, moderate 3–10%, severe > 10%)

Atopic dermatitis extent scoring (component of SCORAD and IGA)

Burn surface area estimation (Rule of Nines for large contiguous areas)

Determining eligibility for biologic or systemic therapy in insurance/guideline contexts

Tracking treatment response at follow-up visits

When NOT to Use as a Sole Measure

BSA alone does not capture lesion severity (thickness, scaling, erythema) — always pair with PASI for psoriasis or EASI for eczema

BSA does not reflect quality-of-life impact — always pair with DLQI, especially for sensitive areas (face, hands, genitalia)

Small BSA involvement in high-impact locations (palms, soles, genitalia) may meet "severe" criteria even with < 3% BSA

Related Scores in Practice

In clinical practice, this assessment is frequently evaluated alongside other validated measures. Depending on the patient's presentation and specific diagnostic requirements, you may also need to utilize the PASI Score, DLQI, EASI Score or the SCORAD to formulate a comprehensive care plan.

Last Comprehensive Review: 2026