1BSA Formulas Explained
DuBois: BSA = 0.007184 × Height^0.725 × Weight^0.425
Boyd: BSA = 0.0003207 × Height^0.3 × Weight^(0.7285 - 0.0188×log10(Weight))
Haycock (paediatric): BSA = 0.024265 × Height^0.3964 × Weight^0.5378
Which Formula to Use?
Mosteller is the most widely used in clinical practice and oncology because of its simplicity (simple square root formula, easy mental math) and validated accuracy. Most chemotherapy dose calculation software uses Mosteller.
DuBois & DuBois (1916) was the original formula, derived from only 9 subjects, and may underestimate BSA in obese patients. Historically used for cardiac index calculation.
Haycock was specifically validated in children from neonates to adults and is the formula of choice for paediatric BSA calculations and paediatric eGFR normalisation.
Clinical Uses of BSA
- Chemotherapy dosing: Most cytotoxic drugs are dosed in mg/m² — carboplatin, doxorubicin, vincristine, paclitaxel. BSA capping at 2.0 m² is common practice to prevent toxicity in obese patients
- Cardiac index (CI): CI = Cardiac Output ÷ BSA. Normal CI = 2.5–4.0 L/min/m². Low CI (<2.2) indicates cardiogenic shock
- eGFR normalisation: CKD-EPI and MDRD give eGFR normalised to 1.73 m² BSA. Multiply by (patient BSA ÷ 1.73) to get absolute GFR in mL/min
- Radiation therapy: BSA used to plan radiation fields and calculate mean doses
BSA Capping in Chemotherapy
In obese patients, using actual BSA for chemotherapy dosing can lead to severe toxicity. Common capping strategies: cap BSA at 2.0 m² (most common), use IBW-based BSA instead of actual weight, or cap dose at standard adult dose. Always check the specific protocol — some regimens (e.g. carboplatin AUC-based dosing) use Calvert formula rather than BSA.
Conversely, underdosing based on capped BSA in obese patients may compromise chemotherapy efficacy. ASCO guidelines recommend using actual body weight (and hence actual BSA) for most chemotherapy regimens in obese patients with performance status.
2Frequently asked questions
What is body surface area used for?
BSA is used to calculate chemotherapy doses (most chemo drugs are dosed per m²), check cardiac index (CI = CO/BSA, normal 2.5–4.0 L/min/m²), calculate renal function (GFR is indexed to 1.73 m² BSA), and dose other drugs with narrow therapeutic windows where weight alone is insufficient.
Which BSA formula is most accurate?
No single formula is universally superior. Mosteller (√[height×weight/3600]) is simplest and widely used. DuBois formula (Weight^0.425 × Height^0.725 × 0.007184) is the historical reference standard. Boyd formula is most accurate in children and extremes of weight. For clinical use, Mosteller is recommended for its simplicity with comparable accuracy to DuBois.
Is BSAbased chemotherapy dosing accurate?
BSA-based dosing reduces inter-patient variability in drug exposure compared to flat dosing, but does not eliminate it. Actual drug clearance is influenced by organ function (renal, hepatic), body composition, genetics (pharmacogenomics), and drug interactions. Many oncology centres now use therapeutic drug monitoring (TDM) for drugs like carboplatin (AUC-based Calvert formula) rather than BSA alone.
What is cardiac index and how does BSA relate to it?
Cardiac index (CI) = Cardiac output (L/min) / BSA (m²). Indexing to BSA accounts for body size differences. Normal CI: 2.5–4.0 L/min/m². CI <2.0 L/min/m² indicates cardiogenic shock. CI is measured by thermodilution (pulmonary artery catheter), echocardiography, or pulse contour analysis. BSA calculation is therefore essential for haemodynamic monitoring in ICU.
How is BSA different from BMI?
BMI = weight/height² — measures weight relative to height as a proxy for body fat. BSA = calculated surface area of the body — used for drug dosing and physiological indexing. BSA accounts for both height and weight differently than BMI and does not assess adiposity. A tall, muscular patient may have high BSA but normal BMI; an obese patient may have elevated BMI and BSA.
What is the normal BSA for Indian adults?
Average BSA for Indian adults: approximately 1.6–1.7 m² for women and 1.7–1.9 m² for men, somewhat lower than the Western reference of 1.73 m² used for GFR indexing. This difference is clinically significant for chemotherapy dosing — Indian oncology guidelines recommend using calculated BSA rather than a fixed value, with capping at 2.0 m² for obese patients in some protocols.
Medical disclaimer: This calculator is for educational and clinical decision-support purposes only. It does not replace clinical judgment or specialist consultation. RxMedCalc is not liable for clinical decisions made solely on this tool.