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.
Calculator
Adjust values & calculateTop 3 Regions (ISS Components)
Formula
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.
Last reviewed: January 2026
Worked Examples
Example 1: Multi-System Trauma Patient
Example 2: Single Region Critical Injury
Background & Theory
The Injury Severity Score Calculator applies the following established principles and formulas. Health and medicine calculators are grounded in validated physiological measurement methods established through decades of clinical research. Body Mass Index, or BMI, is calculated by dividing weight in kilograms by height in meters squared (kg/m²), a formula originating from Adolphe Quetelet's 19th-century statistical work and later codified by the WHO into standard classifications: underweight below 18.5, normal weight 18.5 to 24.9, overweight 25 to 29.9, and obese at 30 and above. Basal Metabolic Rate quantifies the minimum energy required to sustain life at rest. The Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate for most adults, calculates BMR as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) ± sex adjustment. The older Harris-Benedict equations, revised in 1984 by Roza and Shizgal, remain in common use. Total Daily Energy Expenditure is derived by multiplying BMR by a physical activity factor ranging from 1.2 for sedentary individuals to 1.9 for extremely active ones, following the methodology validated by doubly labeled water studies. Body fat percentage can be estimated without laboratory equipment using the U.S. Navy circumference method, which uses neck, waist, and hip measurements, or via BMI-derived equations adjusted for age and sex. The Jackson-Pollock skinfold method offers higher precision with calipers. Blood pressure classification, according to the American College of Cardiology and the 2017 ACC/AHA guidelines, defines normal as below 120/80 mmHg, elevated as 120 to 129 systolic, and hypertension stage 1 as 130 to 139 systolic or 80 to 89 diastolic. Target heart rate zones for aerobic exercise are derived from maximum heart rate estimates, most commonly using the formula 220 minus age in years, with moderate-intensity training typically defined as 50 to 70 percent of maximum heart rate and vigorous intensity at 70 to 85 percent, consistent with CDC and American Heart Association guidelines. These thresholds guide safe and effective cardiovascular conditioning.
History
The history behind the Injury Severity Score Calculator traces back through the following developments. The history of health measurement stretches back to ancient Greece, where Hippocrates around 400 BCE laid the foundation for observational medicine by systematically recording patient symptoms, diet, and environment. His humoral theory, though scientifically superseded, established the principle that the body operates as an interconnected system subject to measurable imbalance. The transformation toward modern medicine accelerated in the 19th century. Louis Pasteur and Robert Koch developed germ theory in the 1860s and 1870s, identifying microorganisms as disease agents and enabling targeted interventions. Florence Nightingale, working during the Crimean War in the 1850s, introduced statistical analysis to nursing practice, demonstrating through data visualization that sanitation reduced mortality. Her work is foundational to evidence-based health measurement. The discovery of vitamins in the early 20th century, beginning with Casimir Funk's coinage of the term in 1912 and culminating in the isolation of vitamins A through K, created the field of nutritional science and gave rise to dietary reference intake frameworks. The World Health Organization, founded in 1948, subsequently established global standards for health metrics, disease classification through the International Classification of Diseases, and recommended daily allowances. The BMI as a clinical screening tool gained traction in the 1970s through Ancel Keys' large-scale epidemiological work, which validated Quetelet's index as a population-level obesity indicator. Through the 1980s and 1990s, the Framingham Heart Study produced landmark data linking cholesterol, blood pressure, and lifestyle factors to cardiovascular disease risk, directly shaping the numeric thresholds still used in health calculators. The evidence-based medicine movement, formalized by Gordon Guyatt and colleagues at McMaster University in the early 1990s, demanded that all health recommendations derive from systematically graded clinical evidence. The digital health era beginning in the 2000s brought these formulas to consumer devices, wearable sensors, and smartphone applications, expanding access to health self-monitoring on a global scale and enabling population-level data collection that continues to refine clinical reference ranges.
Frequently Asked Questions
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.
How do I verify Injury Severity Score Calculator's result independently?
The Formula section on this page shows the equation used. You can reproduce the calculation manually or in a spreadsheet using those steps. Compare your answer against the worked examples in the Examples section, which use known reference values so you can confirm the calculator is behaving as expected.
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.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy