The Psoriasis Area and Severity Index (PASI) is the standard score for how much psoriasis a person has and how severe it is. Use the PASI calculator below: score redness, thickness and scaling from 0 to 4 and the area affected from 0 to 6 for each of the four body regions, and the PASI score updates as you go, with the working shown.
The short answer
- PASI scores four body regions: head and neck, upper limbs, trunk and lower limbs.
- Each region gets 0 to 4 for redness, thickness and scaling, and 0 to 6 for the share of the region affected.
- The formula weights the regions 0.1, 0.2, 0.3 and 0.4 by body surface area, so scores run from 0 to 72.
- A PASI above 10 is severe under Finlay’s Rule of Tens; NICE uses a PASI of 10 or more (with DLQI over 10) for biologic treatment.
- PASI 75 and PASI 90 mean a 75% or 90% fall from the starting score.
Head and neck× 0.1
subtotal 0.0 of 7.2Upper limbs× 0.2
subtotal 0.0 of 14.4Trunk× 0.3
subtotal 0.0 of 21.6Lower limbs× 0.4
subtotal 0.0 of 28.8PASI score
0.0
out of a possible 72
No psoriasis recorded yet. Choose scores for each region; regions you leave at 0 add nothing.
Working
Upper limbs: 0.2 × (0 + 0 + 0) × 0 = 0.0
Trunk: 0.3 × (0 + 0 + 0) × 0 = 0.0
Lower limbs: 0.4 × (0 + 0 + 0) × 0 = 0.0
PASI = 0.0
Enter an earlier PASI to see the change.
For education and record-keeping. It does not diagnose psoriasis or decide treatment. Nothing you enter leaves your browser.
Table of Contents
How to use the PASI calculator
- Pick one region. Start with head and neck, then upper limbs, trunk and lower limbs.
- Score the three signs. Rate redness (erythema), thickness (induration) and scaling (desquamation) from 0 (none) to 4 (very severe) across the psoriasis in that region.
- Score the area. Choose the share of that region covered by psoriasis, from 0 (none) to 6 (90 to 100%).
- Read the result. The PASI score, each region’s subtotal and the full working update as you go. To track treatment, enter an earlier PASI to see the percentage change.
Select a region on the body map to jump to it. Use Copy result to paste the score and working into notes.
How the PASI score is calculated
The PASI formula, as set out in the Indian Journal of Dermatology’s 2023 review of psoriasis assessment, is:
PASI = 0.1 (Eh + Ih + Dh) Ah + 0.2 (Eu + Iu + Du) Au + 0.3 (Et + It + Dt) At + 0.4 (El + Il + Dl) Al
E is erythema (redness), I is induration (thickness), D is desquamation (scaling) and A is the area score. The letters h, u, t and l stand for head, upper limbs, trunk and lower limbs. The British Association of Dermatologists’ PASI worksheet works it in four steps: add the three sign scores for each region, multiply by that region’s area score, multiply by the region’s weight, then add the four regions together.
Severity scores for redness, thickness and scaling
| Score | Severity |
|---|---|
| 0 | None |
| 1 | Slight |
| 2 | Moderate |
| 3 | Severe |
| 4 | Very severe |
Area scores
The area score is the share of that one region affected, not the share of the whole body.
| Score | Share of the region affected |
|---|---|
| 0 | 0% (none) |
| 1 | 1–9% |
| 2 | 10–29% |
| 3 | 30–49% |
| 4 | 50–69% |
| 5 | 70–89% |
| 6 | 90–100% |
Region weights
Each region is multiplied by the amount of body surface area it represents.
| Region | Weight | Highest possible subtotal |
|---|---|---|
| Head and neck | 0.1 | 7.2 |
| Upper limbs | 0.2 | 14.4 |
| Trunk | 0.3 | 21.6 |
| Lower limbs | 0.4 | 28.8 |
Worked example
A person with psoriasis on all four regions might be scored like this:
| Region | Redness + thickness + scaling | Area score | Subtotal |
|---|---|---|---|
| Head and neck | 2 + 1 + 1 = 4 | 2 | 0.1 × 4 × 2 = 0.8 |
| Upper limbs | 2 + 2 + 1 = 5 | 2 | 0.2 × 5 × 2 = 2.0 |
| Trunk | 1 + 1 + 1 = 3 | 1 | 0.3 × 3 × 1 = 0.9 |
| Lower limbs | 3 + 2 + 2 = 7 | 3 | 0.4 × 7 × 3 = 8.4 |
Adding the four subtotals gives 0.8 + 2.0 + 0.9 + 8.4 = PASI 12.1. The lower limbs carry the most weight, so they produce most of this score.
What does a PASI score mean?
A PASI of 0 means no psoriasis was recorded. The maximum is 72, which needs every sign scored 4 and every region scored 6. There is no official PASI band table. Two thresholds come up again and again in UK practice:
| Threshold | What it says | Source |
|---|---|---|
| PASI above 10 | Severe psoriasis, as is a body surface area above 10% or a DLQI above 10 (the “Rule of Tens”) | Finlay, British Journal of Dermatology, 2005 |
| PASI 10 or more | Part of the definition of severe plaque psoriasis for biologic treatment, together with a DLQI above 10 and no response to standard systemic treatments and phototherapy | NICE TA350 (secukinumab), for example |
Because these rules pair PASI with quality of life, a PASI score is usually read alongside the Dermatology Life Quality Index (DLQI).
PASI 50, PASI 75, PASI 90 and PASI 100
Treatment response is measured as the percentage fall from the starting (baseline) PASI. PASI 75 means at least a 75% reduction in the baseline score. PASI 50, 90 and 100 follow the same pattern; PASI 100 means no psoriasis is recorded.
| Response | Fall from baseline | Example from a baseline of 20 |
|---|---|---|
| PASI 50 | 50% or more | 10 or lower |
| PASI 75 | 75% or more | 5 or lower |
| PASI 90 | 90% or more | 2 or lower |
| PASI 100 | 100% | 0 |
NICE uses these changes when reviewing treatment. For methotrexate and ciclosporin it advises assessing the response after 3 months and stopping if it is inadequate, for example a fall of less than 75% in PASI, or a fall of less than 50% in PASI together with less than 5 points on the DLQI (NICE CG153). The calculator’s Compare with an earlier PASI box shows which level a new score reaches.
Limitations of the PASI
- Not validated in children. NICE notes that PASI and body surface area are not validated for use in children and young people (NICE CG153).
- Redness on darker skin. NICE warns that erythema may be underestimated in people with darker skin types, such as Fitzpatrick skin types 5 and 6.
- Judgment and practice. Every input is a judgment by the person scoring, from the redness grade to the share of a region affected, so scoring takes practice. NICE recommends PASI in specialist settings.
- Signs only. PASI measures what is visible on the skin. It does not measure how psoriasis affects daily life, which is why it is paired with the DLQI or the Psoriasis Disability Index (PDI).
PASI and other psoriasis measures
| Measure | What it scores | Range | Who completes it |
|---|---|---|---|
| PASI | Redness, thickness, scaling and area in four body regions | 0 to 72 | Clinician |
| Body surface area (BSA) | Percentage of skin affected, based on the rule of nines | 0 to 100% | Clinician |
| Physician’s Global Assessment (PGA) | Overall severity from clear to very severe; does not measure area | 0 to 5 | Clinician |
| DLQI | Effect of skin disease on quality of life over the last week | 0 to 30 | Patient (10 questions) |
| PDI | Effect of psoriasis on daily life | 0 to 45 | Patient (15 questions) |
PGA and BSA details: Indian Journal of Dermatology, 2023. For the full family of Cardiff questionnaires, see our guide to dermatology quality of life questionnaires.
Where the PASI came from
Torsten Fredriksson and Ulf Pettersson introduced the PASI in 1978, in a trial of an oral retinoid for severe psoriasis published in Dermatologica (PubMed). They described it as “a new index, psoriasis area and severity index (PASI) based on severity and area of psoriatic lesions” and used it to measure 27 patients with severe chronic generalized psoriasis. The paper reports a more than 90% reduction of psoriatic lesions in 10 of 20 patients after 4 to 8 weeks of treatment.
Frequently asked questions
How do you interpret a PASI score?
What is considered a high PASI score?
Is a PASI score of 72 severe?
What does PASI 75 mean?
What does PASI 90 mean?
What is a PASI score of 4?
Can I work out my own PASI score?
Is the PASI used for children?
References
- Fredriksson T, Pettersson U. Severe psoriasis: oral therapy with a new retinoid. Dermatologica. 1978;157(4):238-44. PubMed 357213
- Finlay AY. Current severe psoriasis and the rule of tens. Br J Dermatol. 2005;152(5):861-7. PubMed 15888138
- NICE. Psoriasis: assessment and management (CG153). nice.org.uk
- NICE. Secukinumab for treating moderate to severe plaque psoriasis (TA350). nice.org.uk
- British Association of Dermatologists. Psoriasis Area and Severity Index (PASI) worksheet. PDF
- Manchanda Y, et al. Disease assessment in psoriasis. Indian J Dermatol. 2023. PMC10389140
- DermNet. PASI score. dermnetnz.org