What Is Burn Area Ratio Based on Body Surface Area?
Body surface area (BSA) is the total area of skin covering the body, and in burn care, the ratio of burned area to total BSA (TBSA) is a key indicator for treatment decisions. This calculator uses the Mosteller formula (BSA = √(height(cm) × weight(kg) ÷ 3600)) to estimate your BSA, then applies the widely used "Rule of Nines" from emergency medicine to estimate your burn ratio.
The Rule of Nines
The Rule of Nines divides the adult body into 9% units (or multiples) to quickly estimate burn extent. The head and neck account for 9%, each arm for 9% (18% total), the front and back torso for 18% each (36% total), each leg for 18% (36% total), and the groin for 1%, adding up to 100%. Selecting the burned regions shows both the ratio and the actual area in square meters.
How Burn Severity Is Classified
For adults, burns covering under 10% of BSA are generally classified as minor, though medical care may still be needed depending on the wound's location and depth. Burns of 10-20% are considered moderate and typically require hospital treatment. Burns of 20% or more, or burns affecting the face, hands, or genitals, or suspected inhalation injury, require immediate emergency room and burn center care.
Important Notes
This calculator provides a rough reference estimate for general awareness. The actual depth and extent of a burn, as well as the treatment plan, must always be determined through direct medical examination. Regardless of the calculated result, cool the burn with running cool water immediately and seek medical attention.
Frequently Asked Questions
We calculate BSA using the Mosteller formula, then apply the Rule of Nines to estimate the burn ratio (%) based on the regions you select.
For adults, 10% or more of BSA generally warrants medical care, while 20% or more, or burns to the face, hands, or genitals, require emergency room care.
It divides the adult body into 9% units to quickly estimate burn extent: head 9%, each arm 9%, each leg 18%, front and back torso 18% each, and groin 1%.