PASI Score Calculator (Psoriasis)

PASI stands for Psoriasis Area and Severity Index. It is the most widely used clinical tool to measure the severity of psoriasis by combining the extent of skin involvement with the intensity of three signs — redness (erythema), thickness (induration), and scaling (desquamation) — across four body regions: head, arms, trunk, and legs. Scores range from 0 (clear) to 72 (maximum severity).

Each body region is scored by multiplying the sum of its three severity ratings (erythema + induration + desquamation, each 0–4) by its area score (0–6), then by a body surface weighting factor: head = 0.1, arms = 0.2, trunk = 0.3, legs = 0.4. The four regional subscores are summed to produce the total PASI score.

A PASI of 0 means the skin is clear. Scores of 1–5 indicate mild psoriasis, 6–10 moderate, 11–20 severe, and above 20 very severe psoriasis. A score below 2 is often considered near-complete clearance in clinical trials, and a reduction of 75% from baseline (PASI 75) is a common treatment benchmark.

The area score reflects the percentage of that body region's skin affected by psoriasis: 0 = none, 1 = less than 10%, 2 = 10–29%, 3 = 30–49%, 4 = 50–69%, 5 = 70–89%, and 6 = 90–100%.

Each of the three clinical signs — redness, thickness, and scaling — is rated on a 0–4 scale: 0 = none, 1 = slight, 2 = moderate, 3 = severe, and 4 = very severe. These ratings should reflect the most representative lesion in the region, not the worst or best patch.

This calculator is intended as an educational and reference tool for healthcare professionals and patients. While it implements the standard PASI formula, clinical assessments should always be performed by a qualified dermatologist or healthcare provider who can examine the patient directly.

PASI 75 refers to a 75% reduction in PASI score from a patient's baseline measurement. It is the standard endpoint used in most clinical trials to evaluate the effectiveness of psoriasis treatments. Many newer biologics achieve PASI 90 or even PASI 100 (complete clearance) response rates.

Yes. Other assessments include the Body Surface Area (BSA) score, the Physician Global Assessment (PGA), the Dermatology Life Quality Index (DLQI), and the Psoriasis Symptom Inventory (PSI). PASI remains the gold standard for measuring disease severity in clinical trials, but these alternatives are sometimes used alongside it for a more comprehensive picture.