PASI calculator (Psoriasis Area and Severity Index)

The PASI measures plaque psoriasis severity from 0 to 72. Rate erythema, induration and desquamation (0–4) and the affected area (0–6) per region – the calculator applies the weights.

⚠︎ Learning tool for medical education – not for use in patients or for treatment decisions.

Calculator

Findings per body region Signs 0 = none, 1 = slight, 2 = moderate, 3 = marked, 4 = very marked
ErythemaIndurationDesquamationArea
Head/neck
Upper limbs
Trunk
Lower limbs
–points

🔒 Calculated only in your browser – nothing is stored or transmitted.

Classification (original publication)

ScoreClassification (original publication)
0Clear
0.1–10Mild psoriasis (rule of tens) – provided BSA ≤ 10% and DLQI ≤ 10 as well
> 10Moderate-to-severe psoriasis – Finlay rule of tens: PASI > 10 or BSA > 10% or DLQI > 10

How the PASI is calculated

For each of the four regions, the sum of erythema, induration and desquamation (0–4 each) is multiplied by the area score (0–6) and weighted: head 0.1 · upper limbs 0.2 · trunk 0.3 · lower limbs 0.4. The four sub-scores add up to the PASI (maximum 72).

Area score: 0 = none, 1 = <10%, 2 = 10–29%, 3 = 30–49%, 4 = 50–69%, 5 = 70–89%, 6 = 90–100% of the region.

PASI over time

Trials report change as PASI 75, PASI 90 or PASI 100, i.e. a 75, 90 or 100% reduction from baseline. The PASI is insensitive in limited disease and captures scalp, nails, genitals, palms and soles poorly.

FAQ

Which PASI indicates moderate-to-severe psoriasis?▾

According to the rule of tens (Finlay 2005), psoriasis is moderate-to-severe if PASI, BSA or DLQI exceed 10. Involvement of special sites can upgrade the classification regardless of PASI.

What is the difference between PASI 75 and absolute PASI?▾

PASI 75 describes a 75% reduction from baseline, the absolute PASI the current value.

What is the maximum PASI?▾

72 points: every region with 3 × 4 = 12 severity points and area score 6, weighted by 0.1 + 0.2 + 0.3 + 0.4 = 1.0.

References

  1. Fredriksson T, Pettersson U. Severe psoriasis – oral therapy with a new retinoid. Dermatologica 1978;157:238–44. · PubMed
  2. Finlay AY. Current severe psoriasis and the rule of tens. Br J Dermatol 2005;152:861–7. · PubMed

More Dermatology calculators

EASI calculatorModified Rodnan skin score (mRSS)BSA calculator (affected body surface area)IHS4 calculator (hidradenitis suppurativa)UAS7 calculator (urticaria activity)

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In DermaFuchs you practise PASI, EASI, mRSS, IHS4, UAS7 and more – and learn dermatology with flashcards, spot diagnoses and a dermoscopy course.

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Intended purpose: learning tool for medical education only. Not intended for use in patients or for diagnostic or treatment decisions; not a medical device. Calculations follow the cited original publications; no guarantee of completeness or correctness. Last updated: 09/2026 · Dr. Pascal Bafteh