Injury Severity Score (ISS) Calculator
Enter the highest Abbreviated Injury Scale (AIS) score for each body region. Use 0 if no injury in that region.
What is the ISS score?
The Injury Severity Score (ISS) is a trauma scoring system used to summarize how severely a patient is injured. It converts detailed injury coding into a single number that can be used for clinical communication, outcomes research, trauma registry analysis, and risk adjustment.
ISS is based on the Abbreviated Injury Scale (AIS), where injuries are graded from 1 (minor) to 6 (maximal/unsurvivable) in different body regions.
How ISS is calculated
- Identify the highest AIS score in each of the six ISS body regions.
- Select the three regions with the highest AIS values.
- Square each of those three AIS scores and add them.
Formula: ISS = A² + B² + C² (where A, B, and C are the three highest regional AIS values)
Special rule: if any AIS = 6, ISS is automatically set to 75 (the maximum possible ISS).
ISS body regions
- Head/Neck
- Face
- Chest
- Abdomen or Pelvic Contents
- Extremities or Pelvic Girdle
- External
How to interpret ISS ranges
- 0: No injury recorded
- 1-8: Minor trauma
- 9-15: Moderate trauma
- 16-24: Severe trauma (commonly used threshold for major trauma)
- 25-49: Very severe trauma
- 50-74: Critical trauma
- 75: Maximal score (including any AIS 6 injury)
Worked example
Suppose the highest AIS values are:
- Head/Neck = 4
- Chest = 3
- Abdomen = 2
- All others lower than 2
Use the top three values (4, 3, 2):
ISS = 4² + 3² + 2² = 16 + 9 + 4 = 29.
ISS vs. other trauma scores
NISS (New Injury Severity Score)
NISS uses the three highest AIS injuries regardless of body region. ISS uses one injury per region maximum. Because of this, NISS can better capture multiple severe injuries in the same region.
TRISS
TRISS combines ISS with age and physiologic data (like blood pressure and Glasgow Coma Scale) to estimate survival probability. In many trauma systems, ISS is one component of broader risk prediction.
Important limitations
- ISS depends on accurate AIS coding by trained personnel.
- It may underrepresent patients with several severe injuries in one body region.
- It is not a substitute for bedside clinical judgment.
- Scores should be interpreted in context with vitals, imaging, and comorbidities.
When this calculator is useful
- Trauma education and exam prep
- Quick quality improvement checks
- Research planning and registry familiarization
- Clinical discussions where standardized severity language helps
Disclaimer: This tool is for educational and informational use. It does not provide medical diagnosis or treatment advice.