Body Surface Area Calculator — BSA for Drug Dosing & Clinical Use
Calculate your body surface area (BSA) in m² using the DuBois, Mosteller, or Haycock formula. Used clinically for chemotherapy dosing, burn assessment, cardiac index, and renal clearance calculations.
The original BSA formula, still the most widely used in clinical practice for drug dosing and cardiac output calculations.
| Formula | BSA (m²) | Best used for |
|---|---|---|
| DuBois (1916) | 2.019 | Adults, cardiac output |
| Mosteller (1987) | 2.036 | Adults, oncology/chemo |
| Haycock (1978) | 2.049 | Children, pediatric dosing |
BSA is used to dose chemotherapy drugs (mg/m²), calculate cardiac index, normalize GFR, and assess burn coverage. Always confirm dosing calculations with a pharmacist or treating clinician — never self-dose based on a calculated BSA.
How to use this BSA calculator
Enter your sex, age, height, and weight. Select the formula you need — DuBois is the most widely used in clinical practice, Mosteller is common in oncology, and Haycock is preferred for children. All three results are shown for comparison. Toggle between Imperial (ft/in, lbs) and Metric (cm, kg) above. BSA is expressed in square meters (m²).
Understanding your BSA result
Body surface area (BSA) estimates the total external surface of your body in square meters. Unlike BMI, BSA scales with metabolic capacity, organ volume, and the distribution of drugs through the body. The average adult male has a BSA of approximately 1.9 m² and the average adult female approximately 1.6–1.7 m². These averages are used in clinical dosing tables when a patient's actual BSA is unknown. For drug dosing, always confirm with a pharmacist or prescribing clinician.
Frequently asked questions
BSA reference ranges by age and sex
Body surface area increases with age during childhood, then stabilizes in adulthood. Adult males average around 1.9 m² and adult females around 1.6–1.7 m². These are the most commonly cited reference values in clinical drug dosing literature.
| Age / Group | Average BSA (m²) | Range | Clinical notes |
|---|---|---|---|
| Newborn (3.5 kg) | 0.23 | 0.19–0.27 | Neonatal dosing requires weight-based calculation, not BSA |
| 1 year | 0.47 | 0.40–0.55 | Haycock formula most accurate in this range |
| 2 years | 0.55 | 0.47–0.63 | |
| 5 years | 0.76 | 0.65–0.87 | |
| 10 years | 1.14 | 0.98–1.30 | Pediatric reference point used in many dosing tables |
| 12 years | 1.33 | 1.15–1.52 | |
| Adult female | 1.60–1.70 | 1.45–1.90 | DuBois widely used; 1.73 m² is standard reference value |
| Adult male | 1.85–1.95 | 1.65–2.15 | 1.73 m² or 1.9 m² used as "standard adult" in dosing charts |
| Obese adult (>30 BMI) | 2.1–2.4+ | Variable | BSA-based dosing may require capping in some protocols |
Clinical uses of body surface area
BSA is preferred over simple body weight in situations where the dose-response relationship scales better with surface area than mass — particularly for highly toxic agents where underdosing is ineffective and overdosing is dangerous.
- ·Chemotherapy dosing: most cytotoxic drugs (cisplatin, doxorubicin, paclitaxel, methotrexate) are dosed in mg/m² to normalize for differences in metabolic capacity and organ size between patients
- ·Burn assessment: the Rule of Nines and Lund-Browder chart express burn area as a percentage of BSA — critical for estimating fluid resuscitation needs (Parkland formula: 4 mL × weight kg × %BSA burned)
- ·Cardiac index: cardiac output (liters/min) divided by BSA gives cardiac index (L/min/m²) — a body-size-normalized measure of heart performance; normal range 2.5–4.0 L/min/m²
- ·Renal clearance: glomerular filtration rate (GFR) is conventionally normalized to 1.73 m² BSA, which is why GFR lab results say "per 1.73 m²" — allowing comparison across body sizes
- ·Radiation therapy: some dosing protocols normalize radiation fields to BSA to account for organ volume differences between patients
- ·Pediatric pharmacology: children's drug doses are often scaled from adult doses using the ratio of child BSA to adult BSA (typically 1.73 m²)
Formula comparison — DuBois vs. Mosteller vs. Haycock
All three formulas produce similar results for average-sized adults. Differences become more meaningful at the extremes of height and weight, and especially in pediatric populations.
| Formula | Year | Equation | Best for | Notes |
|---|---|---|---|---|
| DuBois & DuBois | 1916 | 0.007184 × H^0.725 × W^0.425 | Average adults, cardiac output | Based on only 9 subjects; still most widely used clinically |
| Mosteller | 1987 | √(H × W / 3600) | Adults, oncology/chemo dosing | Excellent agreement with DuBois; easiest to calculate manually |
| Haycock | 1978 | 0.024265 × H^0.3964 × W^0.5378 | Children, pediatric dosing | Best validated across body sizes from neonates to adults |
BSA vs. BMI — why BSA matters more in clinical settings
BMI and BSA both use height and weight, but they answer completely different questions and have different clinical applications.
- ·BMI (kg/m²) is a population-level screening tool for adiposity — it estimates the degree of overweight or obesity relative to height squared
- ·BSA (m²) estimates the actual physical surface area of the body — it correlates with metabolic rate, organ volume, and the distribution of toxic drugs
- ·A very tall person and a very short obese person might have similar BMIs but radically different BSAs — and would need very different chemotherapy doses
- ·BMI is poor for clinical drug dosing because it does not account for the metabolic scaling that governs how drugs are processed by the liver and kidneys
- ·BSA is also not perfect: it doesn't account for body composition (fat vs. muscle), which affects how some drugs distribute in the body
- ·Lean Body Mass (LBM) is increasingly proposed as an alternative to BSA for dosing highly lipophilic drugs, but BSA remains the clinical standard for most oncology protocols
How burns are assessed using BSA — the Rule of Nines
The Rule of Nines is a rapid bedside tool that divides the body surface into regions each representing approximately 9% (or multiples thereof) of total BSA. It is used to estimate burn coverage for fluid resuscitation and prognosis.
| Body region | Adult BSA (%) | Pediatric note |
|---|---|---|
| Head and neck | 9% | Larger in infants — up to 18% at birth (Lund-Browder table used instead) |
| Each arm (whole) | 9% | 9% each arm |
| Anterior trunk (chest + abdomen) | 18% | Front of torso |
| Posterior trunk (back) | 18% | Back of torso |
| Each leg (whole) | 18% | 14% in young children |
| Perineum/genitalia | 1% | Constant across ages |
| Total body | 100% | Basis for Parkland formula fluid replacement |