BSA Calculator 2026 — Body Surface Area
Instantly calculate Body Surface Area in m² using five clinically validated formulas — Mosteller, Du Bois, Haycock, Gehan & George, and Boyd. Ideal for chemotherapy dosing, paediatric medicine, and cardiac index calculations.
Adult, Paediatric, or Dosing?
Whether you need a general BSA for adults, a paediatric-specific calculation, or a chemotherapy dose based on BSA, pick the tool below to get instant results.
Adult BSA Calculator
Compare all five clinical formulas for your body surface area
Height in centimetres
Weight in kilograms
BSA Result
Five formula comparison and clinical applications
Enter height and weight, then click Calculate Body Surface Area.
Paediatric BSA Calculator
Optimised formulas for children, infants, and neonates
For age-based reference
For percentile reference
Height in centimetres
Weight in kilograms
Paediatric BSA Result
Age-appropriate formulas and dosing references
Enter child’s height and weight, then click Calculate Paediatric BSA.
BSA-Based Drug Dosing
Calculate chemotherapy and other BSA-dosed medications
Patient height
Patient weight
Standard adult oncology dose rates — verify against current protocols
Drug dose per square metre
Total cycles planned
Leave blank to skip
Used to calculate cardiac index (CI = CO ÷ BSA)
Dosing Result
BSA-based dose, total treatment amount, and cardiac index
Enter patient measurements and drug dose, then click Calculate Dose & Cardiac Index.
BSA Formula Comparison
The five main BSA formulas used in clinical practice. For most adults, results differ by less than 2%. Different specialties may prefer different formulas — oncology often uses Du Bois, paediatrics uses Haycock, and the FDA recommends Mosteller for consistency.
| Formula | Equation | Best For |
|---|---|---|
| Mosteller (1987) | √(h·w / 3600) | General clinical use, FDA recommended |
| Du Bois & Du Bois (1916) | 0.007184 × h^0.725 × w^0.425 | Cardiac index, GFR, traditional standard |
| Haycock (1978) | 0.024265 × h^0.3964 × w^0.5378 | Paediatrics, infants, children |
| Gehan & George (1970) | 0.0235 × h^0.42246 × w^0.51456 | Adults across wide weight range |
| Boyd (1935) | 0.0003207 × h^0.3 × w^(0.7285 − 0.0188·log₁₀w) | Infants, extreme weights, research |
BSA Calculator FAQ
Everything clinicians, students, and patients ask about Body Surface Area calculations.
Body Surface Area (BSA) is the total surface area of the human body measured in square metres (m²). It is used in medicine as a more accurate basis than body weight for calculating drug doses, cardiac index, renal function (GFR), and fluid requirements — particularly in chemotherapy, paediatric medicine, and critical care. Average adult male BSA is ~1.9 m² and average adult female BSA is ~1.6 m².
No single formula is universally ‘most accurate’ — they each have strengths. The Mosteller formula is most widely used in clinical practice due to its simplicity. Du Bois & Du Bois is the traditional standard and used for cardiac index. Haycock is preferred in paediatrics, especially for infants. Boyd is considered highly accurate for a wide weight range, and Gehan & George performs well across adult populations. For most clinical purposes, the results differ by less than 2% between formulas.
Many chemotherapy drugs are dosed in mg/m² rather than mg/kg. The total dose is calculated by multiplying the drug’s BSA-based dose rate by the patient’s BSA. For example, if a drug is prescribed at 75 mg/m² and the patient’s BSA is 1.8 m², the total dose is 75 × 1.8 = 135 mg. This BSA calculator includes a dedicated dosing panel that applies the calculated BSA to common chemotherapy dose rates automatically.
The Mosteller formula is: BSA (m²) = √((height in cm × weight in kg) / 3600). It was published in 1987 by Dr. Robert D. Mosteller in the New England Journal of Medicine and is recommended by the FDA for clinical use. Its simplicity (just one square root operation) makes it the easiest to calculate manually, and it correlates well with the more complex Du Bois formula.
Cardiac index (CI) is cardiac output normalised to body surface area, expressed in L/min/m². It is calculated as: CI = Cardiac Output (L/min) ÷ BSA (m²). Normal cardiac index ranges from 2.5 to 4.0 L/min/m². This adjustment is important because a larger body requires more blood flow — without BSA normalisation, a 6’4″ athlete and a 5’2″ sedentary adult might appear to have similar cardiac outputs despite very different physiological demands.
For children, measure height in cm and weight in kg, then use the Haycock formula (preferred for paediatrics): BSA = 0.024265 × height^0.3964 × weight^0.5378. For very small infants, the Boyd formula may be more accurate. Paediatric drug dosing often uses mg/m² to account for the non-linear relationship between size and metabolic rate. Always verify dosing against current paediatric formularies (e.g., BNF for Children).
In oncology, BSA is often capped at 2.0 m² for obese patients to prevent chemotherapy overdose, since adipose tissue does not increase drug metabolism proportionally. Some protocols use ideal body weight or adjusted body weight instead. The ASCO (American Society of Clinical Oncology) has historically recommended using actual body weight for full BSA calculation, but institutional protocols vary — always follow your centre’s specific policy.
BSA is used in some fluid management calculations, particularly in burns (the Parkland formula uses weight, but BSA-normalised approaches exist) and in paediatric maintenance fluids. Maintenance fluid rates of 1500–2000 mL/m²/day are common in paediatric settings. For burns, the Lund-Browder chart uses BSA percentages of body regions to estimate burn extent and guide resuscitation volumes.