How it's calculated
The Rule of Nines assigns each major body region a fixed percentage of total body surface area, split evenly between its anterior (front) and posterior (back) halves — e.g. the head is 9% total, 4.5% on each view. Tapping a region on the diagram selects just that half, so a burn confined to the back of one leg, for example, can be captured without over-counting the front. Children have a proportionally larger head and smaller legs, so their percentages differ from adults. Selected half-regions are summed for an estimated %TBSA.
Rule of Nines — percentage per anterior/posterior half
| Region | Adult (per half) | Child (per half) |
|---|---|---|
| Head & neck | 4.5% | 9% |
| Each arm | 4.5% | 4.5% |
| Trunk | 18% | 18% |
| Each leg | 9% | 6.75% |
| Genitalia / perineum (anterior only) | 1% | 1% |
Clinical use
- Used for rapid initial estimation of %TBSA burned to guide fluid resuscitation calculations (e.g. the Parkland formula) and to help decide whether transfer to a burns centre is indicated.
- Only partial-thickness (second-degree) and full-thickness (third-degree) burns count toward %TBSA — superficial (first-degree, sunburn-type) burns are excluded.
- For burns that only partially cover a region, or for more precise paediatric estimates by age band, a formal Lund-Browder chart is more accurate than the Rule of Nines.
Frequently asked questions
Why is the paediatric Rule of Nines different from the adult version?
A young child's head makes up a proportionally much larger share of total body surface area, and the legs proportionally less, compared to an adult — the paediatric percentages adjust for this.
Does the Rule of Nines include first-degree burns?
No — superficial (first-degree) burns, which involve only the epidermis, are excluded from %TBSA calculations used for fluid resuscitation and severity grading.
What is the Rule of Nines used for after TBSA is estimated?
Most commonly to calculate initial IV fluid resuscitation requirements using a formula such as Parkland, and to help triage which patients need transfer to a specialised burns unit.
References
- American Burn Association. Advanced Burn Life Support (ABLS) Course Manual.
- Wallace AB. The exposure treatment of burns. Lancet. 1951;257(6653):501-504.