Body Surface Area Calculator | BSA, IBW & Adjusted Weight
Calculate body surface area (BSA) using five clinical formulas: Mosteller, DuBois, Haycock, Gehan-George, and Boyd. Also computes Ideal Body Weight (Devine) and Adjusted Body Weight for drug dosing. Used in oncology, anesthesiology, and clinical pharmacy.
Used for Ideal Body Weight calculation
What Is the Body Surface Area Calculator | BSA, IBW & Adjusted Weight?
Body surface area (BSA) is a physiologically meaningful measure used to normalize drug doses, particularly in oncology, renal dosing, and pediatric medicine. Unlike body weight, BSA correlates more closely with cardiac output, kidney function, and metabolic rate, which is why many high-potency drugs with narrow therapeutic windows are dosed in mg/m² rather than mg/kg.
- ›Mosteller formula: the clinical gold standard since 1987. Published in the New England Journal of Medicine, it is used in most oncology protocols and institutional pharmacy systems for its simplicity and strong validation data.
- ›DuBois & DuBois: the original formula from 1916, still referenced in foundational pharmacokinetics literature and many older drug package inserts.
- ›Haycock formula: validated specifically for neonates and children. For adult oncology, Mosteller is preferred; for pediatric dosing, Haycock is often cited.
- ›Boyd formula: performs best at extremes of weight (very obese or very underweight patients) because the exponent adjusts based on the log of body weight.
- ›Adjusted Body Weight: for obese patients (actual weight > IBW), ABW is used for many drugs (aminoglycosides, vancomycin) because adipose tissue does not contribute proportionally to drug distribution.
Formula
Mosteller (1987) — most widely used
BSA = √( Height(cm) × Weight(kg) / 3600 )
DuBois & DuBois (1916) — original formula
BSA = 0.007184 × Height0.725 × Weight0.425
Haycock (1978) — validated for pediatrics
BSA = 0.024265 × Height0.3964 × Weight0.5378
Gehan & George (1970)
BSA = 0.0235 × Height0.42246 × Weight0.51456
Boyd (1935) — accurate at extremes
BSA = 0.0003207 × Height0.3 × Weight(0.7285 − 0.0188 × log₁₀(W))
Ideal Body Weight — Devine (1974)
IBW (male) = 50 + 2.3 × (height in inches − 60)
IBW (female) = 45.5 + 2.3 × (height in inches − 60)
Adjusted Body Weight (obese patients)
ABW = IBW + 0.4 × (Actual Weight − IBW)
How to Use
- 1
Select metric or imperial units.
- 2
Choose biological sex (used for Ideal Body Weight).
- 3
Enter height and actual measured weight.
- 4
Click Calculate BSA to see results from all five clinical formulas.
- 5
Review Ideal Body Weight and Adjusted Body Weight (shown when actual exceeds IBW).
- 6
Use the built-in drug dose helper to compute total dose from a per-m² prescription.
- 1Choose units: Switch between metric (cm, kg) and imperial (ft/in, lb). Conversions are handled automatically.
- 2Select biological sex: Required for the Devine Ideal Body Weight formula, which uses different base weights for males and females.
- 3Enter height and weight: Input the patient's actual (measured) body weight — not self-reported. Accurate measurements are critical for dosing.
- 4Review all five formulas: The bar chart shows how each formula compares. The average across all five gives a consensus estimate when formulas diverge.
- 5Use the drug dose helper: Enter a prescribed dose in mg/m² (or other unit) to calculate the total dose for this patient's BSA using the Mosteller result.
Example Calculation
Example: Adult male, 180 cm, 80 kg
Height: 180 cm | Weight: 80 kg | Sex: Male
Mosteller = √(180 × 80 / 3600) = √4.00 = 2.000 m²
DuBois = 0.007184 × 180⁰·⁷²⁵ × 80⁰·⁴²⁵ = 1.984 m²
Haycock = 0.024265 × 180⁰·³⁹⁶⁴ × 80⁰·⁵³⁷⁸ = 2.003 m²
IBW (Devine) = 50 + 2.3 × (70.87 − 60) = 50 + 2.3 × 10.87 = 75.0 kg
ABW = not needed (80 kg is close to IBW of 75 kg)
Carboplatin 300 mg/m²: 300 × 2.000 = 600 mg total dose
Understanding Body Surface Area | BSA, IBW & Adjusted Weight
Why Five Formulas Exist and Why They Differ
Each BSA formula was derived from a small cohort of subjects measured using cadaveric surface-coat techniques or photographic mapping. DuBois used 9 subjects in 1916; Haycock measured 81 children and adults in 1978; Gehan and George analyzed 401 patients in 1970. Because the original datasets had different demographic compositions, each formula performs best for patients similar to its derivation sample.
The Mosteller Formula: Why It Became the Standard
The Mosteller formula is elegant: BSA (m²) = √(height × weight / 3600). Its 1987 publication in the NEJM provided a bedside calculation that required nothing more than a square root. When compared against the DuBois formula on typical patients, it produced results within 1–2%, making it a clinically acceptable simplification that could be done without a calculator. Electronic health record systems standardized on it, cementing its position.
- ›Cap doses in practice: most institutional oncology protocols cap BSA-calculated doses at a maximum (e.g., BSA ≤ 2.2 m² for obese patients) to prevent overdosing. Always verify protocol-specific capping rules.
- ›Re-dose with weight changes: BSA should be recalculated if a patient's weight changes by more than 10% during a treatment course. Significant weight loss from treatment toxicity can increase effective dose concentrations.
- ›Calvert formula for carboplatin: unlike most agents, carboplatin is dosed using AUC and measured or estimated GFR (Cockcroft-Gault or CKD-EPI), not BSA. BSA is still needed for initial dose caps.
Ideal vs Adjusted vs Actual Weight: When Each Applies
Drug dosing weight selection depends on both the drug and the patient. For hydrophilic drugs (aminoglycosides, vancomycin), use ABW in obese patients because the drug does not distribute into fat. For lipophilic drugs (benzodiazepines, propofol), actual body weight may be more appropriate. IBW is used when actual weight is less than or equal to IBW — in underweight patients, you never dose below actual weight.
Frequently Asked Questions
Which BSA formula should I use for adult oncology dosing?
For adults: use Mosteller. For children under 18 (especially neonates): Haycock is commonly cited in pediatric oncology literature.
- ›Mosteller: recommended for US and European adult oncology protocols
- ›Haycock: cited in pediatric literature, especially neonates and infants
- ›Boyd: considered most accurate for very obese or very underweight patients
- ›DuBois: legacy use; older drug package inserts may reference it
What is Adjusted Body Weight and when is it used?
Common drugs using ABW for dosing in obese patients:
- ›Aminoglycosides (gentamicin, tobramycin): ABW for initial dose
- ›Vancomycin: actual total body weight for initial dose; ABW for toxicity monitoring
- ›Low-molecular-weight heparins (enoxaparin): capped dosing in obesity
- ›Chemotherapy: most protocols cap BSA at 2.0–2.2 m² for very obese patients
How much do the five formulas typically differ?
- ›Normal adults (70 kg, 170 cm): formulas typically agree within 2–3%
- ›Obese patients: Boyd and Gehan-George tend to give higher BSA than Mosteller
- ›Very short patients: DuBois may underestimate relative to Mosteller
- ›Children under 10 kg: Mosteller significantly overestimates; Haycock preferred
Why is BSA used instead of body weight for chemotherapy?
The relationship was established empirically in the 1950s–1970s by observing that toxic dose thresholds for anticancer drugs correlated better with BSA than weight across animal species.
- ›Cardiac output: scales with BSA (~2.5–3.5 L/min/m²)
- ›Glomerular filtration rate: used for carboplatin AUC dosing (Calvert formula)
- ›Hepatic metabolism: some drugs use ideal body weight or ABW instead
You Might Also Like
Explore 360+ Free Calculators
From math and science to finance and everyday life — all free, no account needed.