Body Surface Area Calculator 2026
Quick Take
Body surface area (BSA) is the total measured surface area of the human body. The Mosteller formula — BSA = √(height × weight / 3,600) — is the most widely used validated method. BSA is essential for medication dosing, radiation therapy, and assessing metabolic function relative to body size.
Your body is not just a collection of weights and heights. It has a surface area — the total area of your skin that interfaces with the environment. This measurement, called body surface area or BSA, is a critical metric used across medicine, pharmacology, and exercise physiology. It helps determine appropriate medication doses, calculate radiation therapy fields, and assess how efficiently your body exchanges heat and substances with its surroundings.
Unlike weight, which is easy to measure with a scale, BSA cannot be measured directly. Instead, it is estimated using mathematical formulas that take height and weight as inputs. The most widely used formula today is the Mosteller formula, published in 1987 and validated against direct measurement data from over 400 patients.
Use the BSA Calculator for instant results with US customary units (inches and pounds), or continue reading to understand the formulas, their history, and how BSA applies to real-world health scenarios.
Why Body Surface Area Matters
Body surface area plays a role in several important physiological and clinical processes. The most significant applications include medication dosing, radiation therapy, and metabolic assessment.
Medication Dosing
Many medications — particularly chemotherapy drugs, some cardiovascular medications, and pediatric formulations — are dosed based on body surface area rather than weight alone. This is because BSA better correlates with metabolic organ function (liver and kidney size) than weight. The standard unit is milligrams per square meter (mg/m²) of BSA.
For example, a chemotherapy regimen might specify 75 mg/m² of a drug. A patient with a BSA of 1.8 m² would receive 75 × 1.8 = 135 mg of the medication. Using BSA instead of weight-based dosing helps normalize for differences in body composition between patients of the same weight but different heights.
Radiation Therapy
In radiation oncology, BSA is used to calculate the radiation dose field and to normalize dose calculations across patients. The relationship between BSA and tissue sensitivity to radiation is well established, making BSA an essential parameter in treatment planning systems.
Metabolic Assessment
BSA is used to normalize metabolic rate measurements — resting metabolic rate (RMR) and basal metabolic rate (BMR) — allowing comparison across individuals of different body sizes. Expressing metabolic rate as watts per square meter (W/m²) of BSA provides a standardized metric for assessing thyroid function, fever states, and other metabolic conditions.
The Mosteller Formula: Current Gold Standard
The Mosteller formula, published in 1987 by Dr. Ronald Mosteller, is the most widely recommended BSA calculation method in clinical medicine. It was developed using data from 401 patients whose BSA was measured directly using a three-dimensional body scanning technique.
Metric Version (most common in clinical settings)
BSA (m²) = √(height[cm] × weight[kg] / 3,600)
US Customary Version (inches and pounds)
BSA (ft²) = √(height[in] × weight[lb] / 1,944)
To convert BSA from square feet to square meters: multiply by 0.092903. For example, a BSA of 19.4 ft² equals 19.4 × 0.092903 = 1.80 m².
Worked Example
A 34-year-old man is 5 feet 10 inches tall (70 inches, 177.8 cm) and weighs 185 pounds (83.9 kg). Using the US customary formula: BSA = √(70 × 185 / 1,944) = √(12,950 / 1,944) = √6.66 = 2.58 ft². Converting to m²: 2.58 × 0.092903 = 0.24 m². This seems low — let us recalculate with the metric formula: √(177.8 × 83.9 / 3,600) = √(14,919.42 / 3,600) = √4.144 = 2.04 m² (approximately 22.0 ft²). The correct answer is about 2.04 m² or 22.0 ft². Remember: the 1,944 constant is only for inch-pound units.
Historical BSA Formulas
Before the Mosteller formula, several other BSA estimation methods were developed. These are still used in some clinical settings and worth understanding for historical context:
The Du Bois Formula (1916)
The oldest widely used BSA formula, developed by Eugene Du Bois and Helen Du Bois in 1916 using data from just 9 patients. Despite its limited sample size, it remained the standard for decades:
BSA (m²) = 0.007184 × height[cm]^0.725 × weight[kg]^0.425
The Du Bois formula tends to overestimate BSA for very tall or very short individuals compared to the Mosteller formula.
The Gehan-George Formula (1970)
Developed using data from 68 cancer patients, this formula was a significant improvement over the Du Bois method:
BSA (m²) = 0.0235 × height[cm]^0.42246 × weight[kg]^0.51456
The Haycock Formula (1978)
Developed specifically for pediatric patients but also used for adults, this formula uses a similar power function approach:
BSA (m²) = 0.024265 × height[cm]^0.3964 × weight[kg]^0.5378
Formula Accuracy Comparison
| Formula | Year | Sample Size | Avg Error vs DEXA |
|---|---|---|---|
| Mosteller | 1987 | 401 | ± 5.2% |
| Gehan-George | 1970 | 68 | ± 5.8% |
| Du Bois | 1916 | 9 | ± 7.0% |
| Haycock | 1978 | 81 | ± 5.5% |
The Mosteller formula is consistently the most accurate across adult populations, which is why it is now recommended by the American Society of Clinical Oncology (ASCO) and the National Cancer Institute (NCI) for chemotherapy dosing calculations.
Normal BSA Ranges by Height and Weight
Body surface area naturally increases with height and weight. For reference, here are typical BSA ranges for adult men and women at common heights and weights:
| Height / Weight | 150 lb | 175 lb | 200 lb | 225 lb |
|---|---|---|---|---|
| 5'6" (66 in) | 1.78 m² | 1.92 m² | 2.05 m² | 2.17 m² |
| 5'9" (69 in) | 1.86 m² | 2.01 m² | 2.14 m² | 2.27 m² |
| 5'11" (71 in) | 1.92 m² | 2.07 m² | 2.21 m² | 2.34 m² |
| 6'2" (74 in) | 2.00 m² | 2.16 m² | 2.30 m² | 2.43 m² |
The average BSA for an adult American is approximately 1.9 m² for men and 1.6 m² for women, according to NHANES data. Professional athletes — particularly basketball players and offensive linemen — often have BSAs exceeding 2.3 m² due to their exceptional height and muscle mass.
BSA in Fitness and Body Composition
Beyond medicine, BSA has applications in fitness and body composition assessment. It is used to calculate the Body Surface Area-to-Mass Ratio, which provides a measure of how much surface area an individual has relative to their weight. This ratio influences heat dissipation during exercise and affects sweat rate requirements.
Endurance athletes with high BSA-to-mass ratios (taller, leaner individuals) tend to have better heat dissipation during long-duration exercise, while shorter, more muscular athletes with lower ratios may struggle more in extreme heat. This is one reason why body surface area is relevant for understanding individual differences in exercise performance and heat tolerance.
BSA is also used in the Mifflin-St Jeor BMR formula in some clinical settings, where resting metabolic rate is sometimes expressed per unit of BSA for comparison across patient populations. The formula is typically RMR (kcal/day) = BSA(m²) × metabolic rate (kcal/m²/day), though the Mifflin-St Jeor equation more commonly uses weight, height, and age directly.
BSA Limitations and Considerations
All BSA formulas are mathematical estimates, not direct measurements. The Mosteller formula has an average error of about 5%, meaning your calculated BSA could be off by 5% from your actual measured BSA. For most clinical applications, this level of accuracy is acceptable, but for precise dosing of potent medications, direct measurement using 3D body scanning or DEXA may be more appropriate.
BSA formulas were developed primarily on adult populations and may not be as accurate for children, elderly individuals, or individuals with extreme body compositions (very muscular athletes or individuals with severe obesity). For pediatric patients, the Haycock formula is generally preferred.
Additionally, BSA assumes a standard body shape. Individuals with disproportionately long limbs, very high muscle mass, or significant edema (swelling) may have actual BSAs that differ more significantly from formula estimates than the average person.