Burn Area Calculator (Rule of Nines)

The Rule of Nines is a quick clinical tool for estimating the total body surface area (TBSA) involved in a burn. It divides the adult body into regions that are each approximately 9% of the total skin surface, or multiples of 9.

Head and neck: 9%. Each arm: 9% (18% combined). Anterior trunk (chest + abdomen): 18%. Posterior trunk (upper and lower back): 18%. Each leg: 18% (36% combined). Perineum: 1%. Total = 100%.

For each region, you enter what fraction of that region is burned, from 0 (none) to 100 (the entire region). The TBSA contribution from each region is: region weight * (fraction burned / 100). Add all contributions together for the total TBSA burned.

This calculator is for adults. Children have proportionally larger heads and smaller legs, so the Lund and Browder chart is used for pediatric burns — it adjusts each region by age group.

Burn severity is classified by TBSA in adults: Minor: less than 10% TBSA (second-degree) or any small, isolated first-degree burn. Manageable outpatient. Moderate: 10-20% TBSA or burns involving face, hands, feet, or genitalia. Typically requires hospital admission. Major: over 20% TBSA, or any inhalation injury, or burns with circumferential involvement of a limb. Burn center referral is standard.

TBSA from first-degree burns (superficial redness only, like mild sunburn) is traditionally excluded from the calculation because these heal quickly without significant fluid loss.

The Rule of Nines is a rapid estimate, not a precise measurement. It takes about 30 seconds at the bedside, which matters in trauma care. For a more accurate calculation, the Lund and Browder chart or 3D scanning tools are used when precision is critical for fluid resuscitation volumes.