Free Injury Severity Score Calculator

Introduction to the Injury Severity Score

The Injury Severity Score (ISS) is a widely used anatomical scoring system that underpins this free online ISS score calculator. Designed for trauma severity assessment, it integrates the Abbreviated Injury Scale (AIS) scores from the three most severely injured body regions to deliver a robust metric that correlates with mortality, morbidity, and hospitalization time. An ISS exceeding 15 is commonly defined as major trauma, making this major trauma calculator an essential component of emergency evaluation. Other tools such as the Revised Trauma Score, SOFA, and SAPS II complement the ISS, but the ISS remains the only anatomical scoring system with a proven linear relationship to patient outcomes.

Developed in 1974 by Baker and colleagues, the ISS extends the earlier Abbreviated Injury Scale (AIS) by focusing on the three most severely injured body systems out of six. Instead of merely summing injury codes, it intentionally assigns greater weight to the worst injuries through squaring. This design reflects the clinical reality that even moderate injuries, when combined, can produce a far worse prognosis than each would alone, thereby improving mortality prediction and resource planning.

Anatomical Regions and Severity Scoring

The ISS divides the human body into six predefined regions:

1. Head and neck – includes cervical spine
2. Face – facial skeleton, nose, mouth, eyes, and ears
3. Chest – thoracic spine and diaphragm
4. Abdomen – abdominal organs, lumbar spine, and pelvic contents
5. Extremities or pelvic girdle – pelvic skeleton and limbs
6. External – skin and soft tissue envelope

Within each region, the worst single injury is assigned an AIS severity score using the following scale:

Severity	Score
No injury	0
Minor	1
Moderate	2
Serious	3
Severe	4
Critical	5
Unsurvivable	6

ISS Calculation Method

Once all six regions are scored, the injury severity score calculation proceeds in three steps:

1. Identify the three body regions with the highest AIS scores.
2. Square each of those three scores.
3. Sum the squared values to obtain the ISS.

Special rule: If any region receives a score of 6 (unsurvivable), the ISS is automatically set to the maximum value of 75, regardless of other scores.

Algebraically, let $a$, $b$, and $c$ be the three highest AIS scores (each ≤5 when no unsurvivable injury exists). Then:

$$\text{ISS} = a^{2} + b^{2} + c^{2}$$

The squared terms ensure that high‑severity injuries disproportionately drive the final score, mirroring the observed escalation in mortality risk.

Interpreting the ISS Score

The ISS ranges from 0 to 75. A threshold of >15 is widely accepted to define major trauma, which often warrants intensive care and aggressive intervention. The score correlates linearly with mortality, length of hospital stay, and other severity measures. Based on the classification proposed by Bolorunduro et al., injury severity can be stratified as follows:

ISS Range	Severity Level
<9	Minor
9–15	Moderate
16–24	Severe
≥25	Very severe / profound

Practical Calculation Example

Consider a car‑accident patient whose injuries have been graded by the trauma team:

Body Region	Worst Injury	AIS Score
Head and neck	No injury	0
Face	Minor	1
Chest	Moderate	2
Abdomen	Serious	3
Extremity	No injury	0
External	No injury	0

The three highest scores come from the abdomen (3), chest (2), and face (1). The ISS is computed as:

$$3^{2} + 2^{2} + 1^{2} = 9 + 4 + 1 = 14$$

With an ISS of 14, the patient’s injury burden falls into the moderate category (9–15). This example shows how the ISS score calculator consolidates multi‑system trauma into a single, clinically actionable number.

Clinical Disclaimer

This trauma severity assessment tool is provided for educational and reference purposes. It delivers standardized calculations based on published AIS and ISS criteria, but it should never replace the comprehensive evaluation and professional judgment of a qualified healthcare provider. Always interpret the ISS within the full clinical context.