Psoriasis Area Severity Index Calculator

Work out psoriasis area severity index instantly with clear inputs, formula shown and shareable results.

About Psoriasis Area Severity Index Calculator

Weights the four regional psoriasis subscores by their share of body surface area — 10 percent head, 20 percent arms, 30 percent trunk and 40 percent legs.

Formula

PASI

PASI = 0.1 x head subscore + 0.2 x upper limb + 0.3 x trunk + 0.4 x lower limb, where each subscore = (erythema + induration + scaling) x area grade 0-6. Range 0-72

Worked example

With the default values below, Psoriasis Area Severity Index Calculator returns PASI score of 13.20. Change any input above and every figure here is recalculated in your browser.

Inputs used

Head subscore (erythema + induration + scaling) x area gradeaccepts 0–72: 6
Upper limb subscoreaccepts 0–72: 9
Trunk subscoreaccepts 0–72: 12
Lower limb subscoreaccepts 0–72: 18

Results

PASI score: 13.20
Severity band: Moderate to severe psoriasis (PASI over 10)
Score representing a PASI 75 response: 3.30
Score representing a PASI 90 response: 1.32

Step by step

1Values used
2PASI
3PASI score= 13.20
4Severity band= Moderate to severe psoriasis (PASI over 10)
5Score representing a PASI 75 response= 3.30
6Score representing a PASI 90 response= 1.32

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

What does PASI 75 mean?

A 75 percent reduction from the baseline PASI, the classic primary endpoint in psoriasis trials.

What counts as severe?

PASI above 10, often combined with a Dermatology Life Quality Index above 10, defines moderate to severe disease for systemic therapy.