🧠 The Rule of 9s: Burn Assessment Made Easy for Medical Exams

When a patient presents with burns, one of the first things you’re expected to determine is the total body surface area (TBSA) affected. The Rule of 9s is a quick, clinical tool used to estimate this, and it shows up on nearly every Step 2 CK, EM rotation, and surgery shelf exam.

Today, we’ll break it down using visuals, mnemonics, and formulas that stick.

🔢 What Is the Rule of 9s?

The Rule of 9s divides the adult body into sections, each worth a multiple of 9%. These are added up to quickly estimate TBSA affected by burns.

🧍‍♂️ Rule of 9s Chart for Adults

Body Region	TBSA (%)
Head and neck	9%
Each arm	9%
Each leg	18%
Anterior torso	18%
Posterior torso	18%
Perineum / genitalia	1%

🧠 KOTC Tip: “Head is 9, each limb and side is 9 or 18”

🧑‍⚕️ Pediatric Variation

• Pediatric patients have larger heads proportionally

• Use Lund-Browder chart for accuracy in children

💧 Fluid Resuscitation: Parkland Formula

Used for patients with burns >20% TBSA

Parkland Formula:
💧 4 mL x body weight (kg) x % TBSA burned
→ Give half in first 8 hours, rest over 16 hours

📌 Example:
70 kg adult with 30% TBSA:
4 x 70 x 30 = 8400 mL total fluids

🧠 High-Yield Scenarios

Scenario	Likely TBSA	Key Management
Burns to anterior trunk + both legs	18 + 18 + 18 = 54%	Fluids + ICU transfer
Burns to arm and neck	9 + 9 = 18%	Likely outpatient unless inhalation risk
Electrical burn, small area	Small TBSA	Still monitor for rhabdo, EKG, myoglobinuria

📌 Before You Go…

Burns are hot topics on exams—so burn this into your memory 🔥

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