ISS (Injury Severity Score) Calculator

ISS (Injury Severity Score) Calculator for Critical Care. Higher ISS describes greater anatomic injury burden within the coding system. It is not an individual mortality probability or a field-triage decision. The special AIS-six rule takes precedence over the ordinary sum-of-squares calculation.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

ISS uses the highest externally assigned AIS grade in each of six body regions. It squares and adds the three largest regional grades. A grade of six in any region sets ISS to 75. The form requires one integer from zero through six for every region, with zero indicating no injury.

When to use this calculator

Use the calculator after coding injuries with an authorized AIS edition and an appropriate coding workflow. It supports anatomic severity reporting and educational arithmetic. It does not assign an injury grade, reproduce the AIS dictionary or replace a trauma assessment.

Inputs used

  • Head/neck: highest assigned AIS (0 if uninjured)
  • Face: highest assigned AIS (0 if uninjured)
  • Chest: highest assigned AIS (0 if uninjured)
  • Abdominal/pelvic contents: highest assigned AIS (0 if uninjured)
  • Extremities/pelvic girdle: highest assigned AIS (0 if uninjured)
  • External: highest assigned AIS (0 if uninjured)

Clinical interpretation

Higher ISS describes greater anatomic injury burden within the coding system. It is not an individual mortality probability or a field-triage decision. The special AIS-six rule takes precedence over the ordinary sum-of-squares calculation.

Worked example

Regional grades 4, 4, 3, 0, 0 and 0 give 4 squared + 4 squared + 3 squared = 41. Grades 6, 0, 0, 0, 0 and 0 give 75. Two injuries within the same region do not contribute as separate ISS regions.

Limitations and safety notes

Incorrect regional assignment or mixing AIS editions undermines comparability. The calculator cannot confirm the coding or identify an unrecorded injury. AIS is proprietary: obtain any necessary individual or site permission from AAAM rather than inferring permission from this arithmetic tool.

Frequently asked questions

Does this page assign AIS grades?

No. Enter regional grades already established using authorized AIS coding.

What if several injuries affect one region?

Enter the highest grade in that region once; ISS uses distinct regions.

Why does one AIS-six injury produce 75?

ISS uses a specific override for any maximal AIS grade, rather than squaring six alone.

References

  • Original ISS anatomic severity method: three distinct regions squared and AIS6 override. https://pubmed.ncbi.nlm.nih.gov/4814394/
  • AAAM identity, AIS regional coding basis, six-grade scale and explicit copyright/licensing requirements. https://www.aaam.org/ais/about

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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