PASI Calculator (Psoriasis Area and Severity Index)

PASI score for psoriasis severity across four body regions (0–72).

For educational and clinical reference. Not a substitute for medical judgment. See the medical disclaimer.

Head & neck (×0.1) — Erythema (0–4)

Head & neck (×0.1) — Induration (0–4)

Head & neck (×0.1) — Desquamation (0–4)

Head & neck (×0.1) — Area involved

Upper limbs (×0.2) — Erythema (0–4)

Upper limbs (×0.2) — Induration (0–4)

Upper limbs (×0.2) — Desquamation (0–4)

Upper limbs (×0.2) — Area involved

Trunk (×0.3) — Erythema (0–4)

Trunk (×0.3) — Induration (0–4)

Trunk (×0.3) — Desquamation (0–4)

Trunk (×0.3) — Area involved

Lower limbs (×0.4) — Erythema (0–4)

Lower limbs (×0.4) — Induration (0–4)

Lower limbs (×0.4) — Desquamation (0–4)

Lower limbs (×0.4) — Area involved

PASI

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Severity

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References

Fredriksson T, Pettersson U. Severe psoriasis — oral therapy with a new retinoid. Dermatologica. 1978;157(4):238-244.

How to use

For each region, rate erythema, induration, and desquamation (0–4).
Select the area-involvement band (0–6) for each region.
The weighted PASI (0–72) and severity band update instantly.

Frequently asked questions

What is the PASI?

The Psoriasis Area and Severity Index combines erythema, induration, and desquamation (each 0–4) with the area involved (0–6) across four body regions, weighted by region.

How is the PASI interpreted?

Range 0–72. Commonly < 5 mild, 5–10 moderate, > 10 severe; PASI > 10 typically indicates a candidate for systemic/biologic therapy.

What are PASI 75/90/100?

Treatment-response metrics — the percentage of patients achieving a ≥ 75%, ≥ 90%, or 100% reduction in PASI from baseline.

What is the regional weighting?

Head ×0.1, upper limbs ×0.2, trunk ×0.3, lower limbs ×0.4, reflecting each region’s share of body surface area.

Last updated June 28, 2026