Injury Severity Score Calculator
Calculate the ISS for trauma patients using Abbreviated Injury Scale (AIS) body region scores. Enter values for instant results with step-by-step formulas.
Formula
ISS = AIS1^2 + AIS2^2 + AIS3^2 (top 3 body regions)
The ISS is calculated by identifying the highest AIS score in each of the six body regions, selecting the three regions with the highest scores, squaring each, and summing the results. Scores range from 0 to 75. If any AIS equals 6 (unsurvivable), the ISS is automatically set to 75.
Worked Examples
Example 1: Multi-System Trauma Patient
Problem: A patient has head injury AIS 4 (severe), chest injury AIS 3 (serious), and extremity fractures AIS 2 (moderate). Calculate the ISS.
Solution: ISS = sum of squares of top 3 AIS scores\nHead/Neck: AIS 4, squared = 16\nChest: AIS 3, squared = 9\nExtremities: AIS 2, squared = 4\nISS = 16 + 9 + 4 = 29
Result: ISS: 29 | Severe | Major Trauma | Estimated Mortality: 10-25%
Example 2: Single Region Critical Injury
Problem: A patient has a critical head injury (AIS 5) with minor facial lacerations (AIS 1) and no other injuries. What is the ISS?
Solution: ISS = sum of squares of top 3 AIS scores\nHead/Neck: AIS 5, squared = 25\nFace: AIS 1, squared = 1\nAll others: AIS 0, squared = 0\nISS = 25 + 1 + 0 = 26
Result: ISS: 26 | Severe | Major Trauma | Estimated Mortality: 10-25%
Frequently Asked Questions
What is the Injury Severity Score (ISS) and how is it calculated?
The Injury Severity Score (ISS) is an anatomical scoring system that provides an overall assessment of the severity of injuries in patients with multiple traumatic injuries. Developed by Baker and colleagues in 1974, it is calculated by taking the three most severely injured body regions from the six defined ISS body regions, squaring the highest Abbreviated Injury Scale (AIS) score from each of those three regions, and summing the squares. The ISS ranges from 0 to 75, where 75 represents the maximum score. If any single body region receives an AIS score of 6 (unsurvivable), the ISS is automatically assigned as 75 regardless of other injuries. An ISS greater than 15 is generally considered major trauma.
What is the Abbreviated Injury Scale (AIS) and how does it relate to ISS?
The Abbreviated Injury Scale is an anatomically based consensus-derived global severity scoring system that classifies individual injuries by body region on a six-point ordinal scale. AIS 1 represents minor injury such as superficial lacerations, AIS 2 is moderate like a simple fracture, AIS 3 is serious such as an open fracture, AIS 4 is severe like a small epidural hematoma, AIS 5 is critical such as a ruptured liver with tissue loss, and AIS 6 is unsurvivable like a total transection of the aorta. The AIS is the foundation of the ISS because the ISS squares and sums the three highest AIS scores from different body regions. Accurate AIS coding is essential for valid ISS calculations and requires trained personnel.
What is the difference between ISS and the New Injury Severity Score (NISS)?
The New Injury Severity Score (NISS) was proposed by Osler and colleagues in 1997 as an improvement over the traditional ISS. While the ISS uses the highest AIS score from each of the three most injured body regions, the NISS uses the three highest AIS scores regardless of body region. This means if a patient has two critical injuries in the head region, the NISS would count both, whereas the ISS would only count the highest. Research has shown that the NISS is a better predictor of mortality in patients with penetrating injuries and in patients with multiple injuries within the same body region. However, the traditional ISS remains the most widely used and accepted trauma scoring system worldwide.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.
Can I share or bookmark my calculation?
You can bookmark the calculator page in your browser. Many calculators also display a shareable result summary you can copy. The page URL stays the same so returning to it will bring you back to the same tool.
Can I use Injury Severity Score Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.