Body Surface Area | NovaCalculator

Formula

BSA = √(height × weight / 3600)

The Mosteller formula calculates body surface area in square meters from height (cm) and weight (kg). Other formulas like Du Bois use different mathematical approaches.

Worked Examples

Example 1: Mosteller Formula

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

Solution: Mosteller Formula:\nBSA = √(height × weight / 3600)\n\nBSA = √(180 × 80 / 3600)\nBSA = √(14400 / 3600)\nBSA = √4\nBSA = 2.00 m²\n\nThis 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:\nBSA = 0.007184 × height^0.725 × weight^0.425\n\nBSA = 0.007184 × (180)^0.725 × (80)^0.425\nBSA = 0.007184 × 43.18 × 6.44\nBSA ≈ 2.00 m²\n\nFor 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\n\nDose = 75 mg/m² × 1.85 m²\nDose = 138.75 mg\n\nIn practice, this might be rounded to 140 mg.\n\nThis 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.

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.

What is body composition and why is it better than BMI alone?

Body composition describes what your body is actually made of: skeletal muscle, fat mass, bone mineral density, and water. Unlike BMI — which divides weight by height squared and cannot distinguish a pound of muscle from a pound of fat — body composition identifies whether weight is metabolically active tissue or stored energy. Healthy body fat percentages vary by sex and age: for women, 20-32% is generally considered healthy; for men, 8-19%. Measurement methods include DEXA scans (most accurate, ±1-2%), hydrostatic weighing, Bod Pod air displacement, bioelectrical impedance (consumer scales, ±3-5%), and skinfold calipers. A muscular person with a BMI of 27 (overweight) might have excellent body composition, while a sedentary person with a normal BMI could have metabolically risky visceral fat levels.

Does Body Surface Area work offline?

Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.

Why might my result differ from another tool or reference?

Differences typically arise from rounding conventions, the specific version of a formula (for example, simple vs compound interest), or unit inconsistencies between inputs. Check that both tools are using the same formula variant and the same units. The References section links to the authoritative source behind the formula used here.

What inputs do I need to use Body Surface Area accurately?

Each field is labelled with the required unit (metric or imperial). Gather your source values before starting — for example, a weight measurement in kilograms, a distance in metres, or a dollar amount — and enter them exactly as measured. The formula section on this page lists every variable and explains what each represents.

Background & Theory

The Body Surface Area (BSA) Calculator applies the following established principles and formulas. Clinical medicine relies on standardized measurement tools and formulas to guide diagnosis, dosing, and patient monitoring with precision and reproducibility. Pediatric and weight-sensitive drug dosing is calculated in milligrams per kilogram of body weight, a method that adjusts for physiological variation across patient sizes and ensures therapeutic drug levels without toxicity. This principle extends to adult populations for medications with narrow therapeutic indices, such as aminoglycosides and anticoagulants. Glomerular filtration rate, or GFR, is the primary index of kidney function, estimating how much blood the kidneys filter per minute. The CKD-EPI equation, developed in 2009 and refined in 2021 to remove the race variable, uses serum creatinine, age, and sex to estimate GFR, classifying chronic kidney disease stages from G1 (above 90 mL/min/1.73m²) through G5 (below 15 mL/min/1.73m²). The older Cockcroft-Gault formula remains valuable for calculating creatinine clearance to guide drug dosing. Body surface area is critical for chemotherapy dosing and certain cardiovascular assessments. The Mosteller formula, BSA = square root of (height in cm × weight in kg / 3600), is favored for its computational simplicity and clinical accuracy. Du Bois, Haycock, and Gehan-George formulas are alternatives used in specific pediatric and research settings. Fluid balance calculations track intake against output to guide intravenous therapy, particularly in critical care, surgery recovery, and burn management. The Parkland formula calculates initial fluid resuscitation for burns as 4 mL × weight in kg × percent body surface area burned, delivered over 24 hours. The Glasgow Coma Scale, scored across eye opening, verbal response, and motor response, provides a standardized neurological assessment with scores ranging from 3 (deep coma) to 15 (fully alert). The APGAR score, assessed at one and five minutes after birth across five criteria, quantifies neonatal transition to extrauterine life. Both scales support rapid clinical decision-making and interoperability across care teams.

History

The history behind the Body Surface Area (BSA) Calculator traces back through the following developments. Clinical measurement as a formal discipline emerged from centuries of empirical observation systematized into reproducible tools. The measurement of body temperature became practical following Daniel Gabriel Fahrenheit's development of the mercury thermometer in 1714, which established a calibrated temperature scale. Anders Celsius introduced the centigrade scale in 1742, and Carl Wunderlich's 19th-century hospital surveys of over a million temperature readings established the normal range of 36 to 37.5 degrees Celsius, giving thermometry a clinical reference standard. Blood pressure measurement was transformed by Scipione Riva-Rocci's invention of the arm-cuff sphygmomanometer in 1896, which allowed non-invasive systolic pressure measurement. Nikolai Korotkoff's 1905 description of auscultatory sounds during cuff deflation enabled both systolic and diastolic readings, creating the method still in standard clinical use today. Willem Einthoven's invention of the electrocardiograph in 1901 and his receipt of the Nobel Prize in 1924 formalized cardiac electrical measurement and initiated a century of electrophysiological diagnostics. The first rigorous controlled clinical trial in modern medicine is credited to Austin Bradford Hill and the Medical Research Council streptomycin tuberculosis trial of 1948, which introduced randomization, control groups, and blinding as methodological cornerstones. Hill subsequently developed the criteria for causal inference in epidemiology, shaping how clinical evidence is generated and interpreted. The Glasgow Coma Scale was developed by Graham Teasdale and Bryan Jennett at the University of Glasgow in 1974 as a standardized neurological assessment for trauma patients. The APGAR score was introduced by Virginia Apgar in 1952 as a rapid neonatal assessment tool, originally developed to address inconsistency in delivery room practices. The Mosteller BSA formula was published in 1987, simplifying earlier more complex calculations for routine clinical use. The late 20th century saw the rise of clinical decision support systems embedding these formulas into hospital information technology, reducing calculation errors and improving bedside access to validated tools.