Body Surface Area

Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.

Formula

BSA = √(height × weight / 3600)

The Mosteller formula calculates body surface area in square meters as the square root of height (cm) times weight (kg) divided by 3600. Du Bois and Du Bois instead use 0.007184 × height^0.725 × weight^0.425, and Haycock, Gehan-George and Boyd use their own regression constants. For adults of typical size the five results usually agree within a few percent. Drug dosing based on BSA is a clinical decision: use the value your care team calculates, not this page.

Worked Examples

Example 1: Mosteller Formula

Problem:Calculate BSA for a person 180cm tall and 80kg.

Solution:Mosteller Formula: BSA = √(height × weight / 3600) BSA = √(180 × 80 / 3600) BSA = √(14400 / 3600) BSA = √4 BSA = 2.00 m² This is slightly above average adult BSA.

Result:BSA = 2.00 m² (Large category)

Example 2: Du Bois Formula

Problem:Same person using Du Bois formula.

Solution:Du Bois Formula: BSA = 0.007184 × height^0.725 × weight^0.425 BSA = 0.007184 × (180)^0.725 × (80)^0.425 180^0.725 = 43.15, 80^0.425 = 6.44 BSA = 0.007184 × 43.15 × 6.44 = 1.996 BSA ≈ 2.00 m² For typical adults, Du Bois and Mosteller usually land very close to each other.

Result:BSA ≈ 2.00 m² (Du Bois)

Example 3: Chemotherapy Dosing Example

Problem:A drug is prescribed at 75 mg/m². Patient BSA is 1.85 m². What's the dose?

Solution:Dose = Prescribed dose per m² × BSA Dose = 75 mg/m² × 1.85 m² Dose = 138.75 mg In practice, this might be rounded to 140 mg. This is why accurate BSA matters: a 10% error in BSA causes 10% error in drug dose, which can be significant for toxic drugs.

Result:Dose = 138.75 mg (round to 140 mg)

Frequently Asked Questions

What is body surface area (BSA)?

Body surface area is the total surface area of the human body, measured in square meters (m²). Average adult BSA is approximately 1.7-2.0 m². BSA is used in medicine to normalize physiological parameters and drug dosages that vary with body size.

Why is BSA important in medicine?

BSA is crucial for: 1) Chemotherapy dosing - cancer drugs are highly toxic and dosed precisely per m², 2) Burns assessment - determining fluid replacement needs, 3) Cardiac output indexing, 4) Renal function assessment, 5) Metabolic rate calculations. It provides a more accurate basis for dosing than weight alone.

Which BSA formula is most accurate?

Du Bois & Du Bois (1916) is historically most referenced. Mosteller (1987) is popular due to simplicity. Haycock is often preferred for children. For typical adults, all formulas give similar results (within 5%). In clinical practice, the choice is often institution-specific.

How does BSA differ from BMI?

BMI is weight divided by height squared - a ratio indicating body composition. BSA estimates actual skin surface area - a geometric measurement. BMI classifies body weight status; BSA is used for physiological calculations and drug dosing. They measure different things.

What's the average BSA for adults?

Average adult BSA is approximately 1.7 m² for women and 1.9 m² for men. Normal range is roughly 1.5-2.2 m². Athletes and larger individuals may exceed 2.5 m². BSA increases with both height and weight but is more sensitive to height.

How is BSA used in chemotherapy?

Chemotherapy drugs are highly toxic with narrow therapeutic windows. Dosing by BSA (mg/m²) accounts for body size variations better than fixed doses. A larger person can tolerate more drug while maintaining safe tissue concentrations. This reduces both under-dosing and toxicity.

Can I measure BSA directly?

Direct measurement is impractical. The formulas estimate BSA from height and weight based on historical measurements of cadavers and living subjects. Modern 3D body scanning can measure BSA directly but isn't widely available. Formulas remain the standard approach.

Does BSA change with body composition?

BSA formulas use only height and weight, not body composition. A muscular person and an obese person of the same height and weight would have identical calculated BSA, though their actual surface areas may differ. For extreme body compositions, adjustments may be needed.

Why do different formulas give different results?

Each formula was derived from different study populations and methods. Du Bois used 9 subjects with direct measurement. Mosteller simplified the calculation. Haycock focused on children. The differences are usually small (3-5%) for typical adults but can be larger at extremes.

Should I use BSA for exercise calculations?

For exercise and fitness purposes, BSA isn't typically needed. Use BMR/TDEE for calorie calculations. BSA is primarily a clinical tool. However, BSA does correlate with blood volume and cardiac output, which affect athletic performance at elite levels.

Background & Theory

Body surface area (BSA) estimates the total surface area of the human body. It's essential in clinical medicine for drug dosing, physiological calculations, and medical decision-making.

Major BSA Formulas:

Mosteller (1987) - Simplest:
BSA = √(height(cm) × weight(kg) / 3600)

Du Bois & Du Bois (1916) - Historical Standard:
BSA = 0.007184 × height^0.725 × weight^0.425

Haycock (1978) - Pediatric:
BSA = 0.024265 × height^0.3964 × weight^0.5378

Gehan & George (1970):
BSA = 0.0235 × height^0.42246 × weight^0.51456

Boyd (1935):
BSA = 0.0003207 × height^0.3 × weight(g)^(0.7285 - 0.0188 × log10 weight(g))

Average Adult BSA:

Category	Typical Range
Adult Women	1.5-1.8 m²
Adult Men	1.7-2.1 m²
Children (varies)	0.2-1.5 m²
Large Adults	2.0-2.5 m²

Clinical Applications:

Chemotherapy Dosing:
- Most cancer drugs dosed as mg/m²
- Reduces inter-patient variability
- Critical for safety
Burns Assessment:
- Rule of Nines uses BSA
- Determines fluid replacement
Cardiac Index:
- Cardiac output / BSA
- Normalizes for body size
Renal Function:
- GFR often normalized to 1.73 m²
- Standard adult reference BSA

Formula Selection:

Mosteller: General use, easy calculation
Du Bois: Traditional standard
Haycock: Pediatric patients
For most adults, differences are <5%

History

Body surface area estimation has a century-long history in medicine. In 1879, Meeh proposed the first BSA formula based on geometric principles. The most influential formula came from Du Bois and Du Bois in 1916, derived from direct measurements of 9 subjects using a casting method. For decades, the Du Bois formula remained standard despite its complex exponents. In 1987, Mosteller proposed a simplified formula using a square root calculation that could be done mentally - this became widely adopted due to its simplicity. Pediatric-specific formulas emerged because adult formulas were less accurate for children. Haycock (1978) developed equations for pediatric use, which became standard in pediatric oncology. The importance of BSA grew with chemotherapy development in the 1950s-60s. Cancer drugs were too toxic for fixed dosing, and BSA-based dosing reduced variation in drug exposure. Today, most chemotherapy protocols specify doses in mg/m². Modern debates question whether BSA is optimal for drug dosing. Some argue that organ-specific factors (renal function, liver function) matter more. However, BSA remains the standard for most applications, particularly chemotherapy.