Injury Severity Score (ISS) Calculator
Enter the highest AIS value (0-6) for each body region. The calculator squares and sums the top three region scores to produce ISS. If any region has AIS 6, ISS is automatically 75.
What is the ISS trauma score?
The Injury Severity Score (ISS) is a widely used trauma scoring system that estimates overall injury burden in a patient with multiple injuries. It is based on the Abbreviated Injury Scale (AIS), which rates individual injuries from 1 (minor) to 6 (maximal/unsurvivable).
Clinicians, trauma registries, and researchers use ISS to support triage decisions, compare outcomes between hospitals, and stratify risk in trauma studies.
How ISS is calculated
Step-by-step method
- Assign the highest AIS value in each of the six ISS body regions.
- Identify the three highest region AIS scores.
- Square each of those three values and add them together.
- If any AIS value is 6, ISS is automatically set to 75.
Formula: ISS = A² + B² + C² (where A, B, and C are the top three regional AIS scores).
ISS range
- Minimum: 0 (no coded injuries)
- Maximum: 75
- Major trauma is commonly defined as ISS ≥ 16
Body regions used in ISS
- Head/Neck
- Face
- Chest
- Abdomen or pelvic contents
- Extremities or pelvic girdle
- External
Each region contributes only its single highest AIS value, not all injuries in that region.
How to use this ISS trauma score calculator
- Select an AIS score for each body region.
- Click Calculate ISS.
- Review the ISS value, severity category, and major-trauma flag.
Tip: If you are doing chart abstraction, make sure AIS values come from an official coding source to maintain consistency.
Interpreting the result
ISS helps summarize injury severity, but it should always be interpreted with clinical context. A practical interpretation framework is:
- 1-8: Minor trauma burden
- 9-15: Moderate trauma burden
- 16-24: Severe trauma (major trauma threshold crossed)
- 25-49: Critical trauma burden
- 50-75: Extremely critical / maximal injury burden
ISS vs AIS vs NISS
AIS
AIS scores individual injuries anatomically. It does not provide a whole-patient summary by itself.
ISS
ISS converts regional AIS data into one global severity number, but it only uses one injury per region.
NISS
The New Injury Severity Score (NISS) uses the three highest AIS injuries regardless of body region, which may better capture clustered injuries in one area.
Limitations to know
- ISS depends on correct AIS coding quality.
- It is anatomy-based and does not directly include physiology (e.g., blood pressure, lactate, GCS trends).
- Two patients with the same ISS can have different clinical trajectories.
- Not a standalone predictor of outcome for individual patient decisions.
Clinical reminder
This calculator is for educational and research support use. It does not replace trauma team assessment, institutional protocols, or physician judgment. For urgent or emergency care, follow your local emergency response system immediately.