BSA (Body Surface Area) Calculators

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Body surface area (BSA) is the total surface area of the human body, measured in square meters (m²). It is calculated from height and weight using empirical formulas and is used extensively in medicine for drug dosing — particularly chemotherapy agents, where dosing by BSA rather than body weight accounts for differences in drug distribution, metabolism, and toxicity across patients of different sizes. The average adult BSA is approximately 1.7–1.8 m². Multiple BSA formulas exist; the Mosteller formula is most widely used today due to its simplicity.

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BSA Formulas

Mosteller (most common): BSA (m²) = √[height(cm) × weight(kg) / 3600]

DuBois and DuBois: BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425

Haycock (preferred for children): BSA = 0.024265 × height(cm)^0.3964 × weight(kg)^0.5378

Example using Mosteller: 170 cm, 70 kg: BSA = √(170 × 70 / 3600) = √3.306 = 1.82 m².

BSA in Chemotherapy Dosing

Doses are expressed in mg/m². Example: 100 mg/m² for BSA 1.82 m² = 182 mg total dose. BSA-based dosing aims to normalize drug exposure across patients by adjusting for body size. Some newer agents use flat dosing where PK studies show BSA does not improve dose precision.

BSA vs. BMI

BMI = weight(kg)/height(m)² — assesses weight relative to height; used for obesity classification. BSA measures total skin/metabolic surface area and accounts for height and weight together. They serve different purposes: BMI for weight status; BSA for drug dosing, burn area estimation, and fluid replacement.

Average BSA Values

  • Average adult male: ~1.9 m²
  • Average adult female: ~1.6 m²
  • Child (10 years): ~1.14 m²
  • Newborn: ~0.25 m²

Glossary

Body Surface Area (BSA)
Total skin surface area in m²; Mosteller formula: √(height_cm × weight_kg / 3600); average adult 1.7–1.9 m²; used for chemotherapy dosing, burn care, and cardiac index calculations.
Mosteller Formula
BSA (m²) = √[height(cm) × weight(kg) / 3600]; the most widely used BSA calculation in clinical oncology due to simplicity and accuracy within normal adult ranges.
Rule of Nines
A burn surface area estimation method: head/neck = 9%, each arm = 9%, front trunk = 18%, back trunk = 18%, each leg = 18%, perineum = 1%; used to calculate fluid resuscitation needs.

Frequently Asked Questions

BSA (m²) = √[height(cm) × weight(kg) / 3600]. It is the most widely used BSA formula in clinical practice due to simplicity. Example: patient 165 cm, 60 kg: BSA = √(165 × 60 / 3600) = √2.75 = 1.66 m². Results closely match the more complex DuBois formula across normal adult ranges. In spreadsheets: =SQRT(height_cm * weight_kg / 3600).

BSA-based dosing assumes pharmacokinetic parameters scale with body surface area, so patients with larger BSA need larger doses to achieve equivalent drug exposure and avoid toxicity. Dose (mg) = prescribed dose (mg/m²) × patient BSA (m²). Example: 75 mg/m² for a 1.75 m² patient = 131.25 mg. BSA dosing reduces extreme over- or under-dosing compared to flat dosing, though it is an imperfect predictor of PK for all drugs — some agents now use weight-based or flat dosing based on clinical trial data.

BMI (kg/m²) = weight divided by height squared; classifies weight status (underweight, normal, overweight, obese) for population-level screening. BSA (m²) = √(height × weight / 3600); measures total body surface area for clinical dosing, fluid replacement, and burn assessment. BMI does not account for height and weight combination meaningfully for pharmacokinetics; BSA does. They are mathematically distinct and serve different clinical purposes — BSA is not used for obesity classification, and BMI is not used for drug dosing.

In burns, BSA is used for two purposes: (1) The Rule of Nines estimates percent of total BSA burned: head/neck = 9%; each arm = 9%; chest front = 18%; back = 18%; each leg = 18%; genitals = 1%. (2) Parkland formula for fluid resuscitation: total IV fluids in first 24 hours = 4 mL × weight(kg) × % BSA burned. Half given in first 8 hours, remainder over the next 16 hours. Accurate burn extent assessment is critical because both under- and over-resuscitation cause serious complications.