Body Surface Area Calculator

Body Surface Area Calculator

Body Surface Area (BSA) is the total external surface of the human body measured in square meters, and it plays a central role in clinical medicine where body weight alone is not a reliable dosing proxy. This calculator estimates your BSA using four established formulas — Du Bois, Mosteller, Haycock, and Gehan-George — and presents the results side by side so you can see how different methods compare. The value is used in chemotherapy dosing, burn injury assessment, fluid resuscitation, and cardiac output interpretation.

How BSA Is Calculated

All four formulas take height (in centimeters) and weight (in kilograms) as inputs and return a result in square meters (m2):

• Du Bois (1916): BSA = 0.007184 x height(cm)^0.725 x weight(kg)^0.425
• Mosteller (1987): BSA = sqrt(height(cm) x weight(kg) / 3600)
• Haycock (1978): BSA = 0.024265 x height(cm)^0.3964 x weight(kg)^0.5378
• Gehan-George (1970): BSA = 0.0235 x height(cm)^0.42246 x weight(kg)^0.51456

The Mosteller formula is the simplest to calculate by hand and produces results within 1-2% of Du Bois for average-sized adults. The Haycock formula was specifically validated in pediatric populations and is preferred for children. For adults of average build, all four formulas typically agree within 0.02-0.05 m2.

Worked Examples

Example 1 — Average adult woman. Height 5’5” (165 cm), weight 140 lbs (63.5 kg). Mosteller: sqrt(165 x 63.5 / 3600) = sqrt(2.91) = 1.71 m2. A chemotherapy drug dosed at 50 mg/m2 would call for an 85.5 mg dose.

Example 2 — Tall adult man. Height 6’2” (188 cm), weight 210 lbs (95.3 kg). Du Bois: 0.007184 x 188^0.725 x 95.3^0.425 = approximately 2.28 m2. This is significantly above the standard 1.73 m2 reference value used in GFR calculations.

Example 3 — Pediatric patient. A 10-year-old child at 4’4” (132 cm) and 70 lbs (31.8 kg). Haycock: 0.024265 x 132^0.3964 x 31.8^0.5378 = approximately 1.07 m2. Pediatric drug doses scaled to this BSA would be roughly 62% of a standard adult dose, not 50% — which is why weight-based dosing alone underestimates appropriate pediatric doses.

BSA Reference Values by Height and Weight (Mosteller Formula)

When to Use This Calculator

• Understanding the basis for a mg/m2 chemotherapy or immunotherapy dose your oncologist has prescribed
• Checking a GFR result reported relative to 1.73 m2 BSA — the standard normalization reference for kidney function
• Burn injury assessment using the Rule of Nines to estimate percentage of total BSA affected
• Pediatric dosing calculations where children’s organ function scales more closely with BSA than with weight
• Cardiac index interpretation — normal cardiac index is 2.5-4.0 L/min/m2, which requires your BSA to compute from raw cardiac output

Common Mistakes

1. Confusing BSA with BMI. Both use height and weight, but BMI is a categorical screening tool for weight status while BSA is a continuous physiological measurement used in medical dosing. A BSA of 2.0 m2 carries no weight-status interpretation — it is just a surface area.
2. Using the wrong unit inputs. All four formulas require height in centimeters and weight in kilograms internally. Entering feet/pounds without conversion produces wildly incorrect results. The calculator handles conversion automatically, but if you compute manually, convert first.
3. Assuming one formula is universally correct. No single formula has been validated as definitively superior across all populations. In pediatric oncology, Haycock is preferred; in adult oncology, Mosteller is common; in research, Du Bois remains the historical reference. Use whichever your clinical context specifies.
4. Treating BSA as precise. BSA formulas are regression estimates derived from small historical datasets. The actual surface area of a living person can vary by several percent from the formula result due to differences in body shape and proportions.

Real-World Applications

BSA underpins a wider range of clinical decisions than most people realize. In oncology, virtually all cytotoxic drug protocols specify doses in mg/m2 — a breast cancer patient at 1.65 m2 receiving carboplatin at 300 mg/m2 gets 495 mg, while a patient at 2.05 m2 gets 615 mg. In nephrology, measured GFR values are adjusted to 1.73 m2 BSA so that kidney function can be compared across patients of different sizes. In burn medicine, the Parkland formula for fluid resuscitation is 4 mL x weight(kg) x (%BSA burned), meaning an accurate burn BSA percentage directly determines how many liters of IV Ringer’s lactate a patient receives in the first 24 hours. For burn patients with greater than 20% BSA involvement, this is a life-sustaining calculation.

Tips

1. For a quick mental estimate, a 5’7” adult weighing 155 lbs has a BSA close to the 1.73 m2 standard reference — anyone taller or heavier will be above it
2. The Mosteller formula can be computed in seconds with a basic calculator: multiply height(cm) by weight(kg), divide by 3600, then take the square root
3. When following a chemotherapy protocol, ask your care team which formula their pharmacy system uses — consistency across cycles matters more than formula choice
4. BSA changes slowly with weight; a 10-lb weight change shifts BSA by roughly 0.04-0.06 m2, which may not affect a rounded mg/m2 dose
5. For children, always prefer the Haycock formula — it was specifically validated in patients from 0.1 m2 to 2.2 m2 across all pediatric age groups
6. This calculator is for educational reference; all treatment dosing decisions must be confirmed by a licensed healthcare provider using your full clinical picture