PASI Score Calculator
Enter the psoriasis severity for each body region. This calculator uses the standard PASI method: PASI = 0.1(Head) + 0.2(Arms) + 0.3(Trunk) + 0.4(Legs), where each regional score is (Erythema + Induration + Scaling) × Area Score.
What is the PASI score?
PASI stands for Psoriasis Area and Severity Index. It is one of the most widely used tools for measuring psoriasis severity in both clinical practice and research. The final PASI value ranges from 0 to 72, where higher values represent more severe disease.
The score combines two important dimensions:
- How severe plaques look (redness, thickness, and scaling)
- How much skin is involved in each body region
How this PASI score calculator works
1) Score lesion severity in each region
For each region, rate the following from 0 to 4:
- Erythema (redness)
- Induration (thickness/infiltration)
- Scaling (desquamation)
Add these three values to get a regional severity sum (0 to 12).
2) Convert area percentage to PASI area score
You enter area as a percentage (0 to 100%) and the calculator converts it to the PASI area score (0 to 6):
| Area involved in a region | Area score |
|---|---|
| 0% | 0 |
| <10% | 1 |
| 10-29% | 2 |
| 30-49% | 3 |
| 50-69% | 4 |
| 70-89% | 5 |
| 90-100% | 6 |
3) Apply body-region weights
Each region contributes differently to total PASI:
- Head/Neck: 0.1
- Upper Limbs: 0.2
- Trunk: 0.3
- Lower Limbs: 0.4
Regional PASI = (E + I + S) × Area score × Region weight. Total PASI = sum of all 4 regional scores.
How to interpret PASI values
There is no single universal cut-point for every context, but a common practical interpretation is:
- Mild: PASI < 7
- Moderate: PASI 7 to 12
- Severe: PASI > 12
In trials, treatment response is often reported as PASI 75, PASI 90, or PASI 100, meaning 75%, 90%, or 100% improvement from baseline.
Why PASI is useful
- Provides a standardized way to track disease over time
- Helps compare outcomes before and after treatment
- Commonly used in dermatology studies and biologic therapy trials
- Captures both lesion severity and body surface distribution
Limitations to keep in mind
PASI is very helpful, but it is not perfect. It can be less sensitive in patients with low body surface area involvement, and inter-rater variability can occur when different clinicians score redness, thickness, or scale differently.
Also, PASI does not directly measure symptoms like itch, pain, sleep disturbance, or quality of life. In real care, clinicians often combine PASI with patient-reported outcomes and clinical judgment.
Practical tips for more consistent scoring
- Use similar lighting and exam conditions each visit
- Score the same anatomic areas in a consistent pattern
- Document baseline photos when appropriate
- Avoid estimating area too quickly—use handprint or region-based visual guides
- Pair PASI trends with symptom and quality-of-life tracking
Medical disclaimer
This PASI score calculator is for educational and tracking purposes only and does not replace diagnosis, treatment planning, or advice from a qualified healthcare professional. If you have psoriasis or worsening skin symptoms, consult a licensed dermatologist.