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Pharmaceutical Calculators

BMI & BSA Calculator

Calculate Body Mass Index and Body Surface Area using DuBois, Mosteller, and Haycock formulas. Essential for oncology chemotherapy dosing and clinical weight assessments.

Key Formulas
BMI = Weightkg / Heightm²
BSA(DuBois) = 0.007184 × H0.725 × W0.425
BSA(Mosteller) = √(H × W / 3600)
BSA(Haycock) = 0.024265 × H0.3964 × W0.5378
H = height in cm    W = weight in kg    BSA in m²
BMI
—
kg/m²
Body Surface Area (BSA)
DuBois Primary
—
m²
Mosteller
—
m²
Haycock Pediatric
—
m²
IBW
—
kg
Oncology Dosing Note: BSA-based chemotherapy dosing uses DuBois or Mosteller. For capped dosing, confirm the institution's cap policy (typically 2.0 m²).

How to Use

1
Enter weight and select the unit (kg or lbs). The calculator converts automatically.
2
Enter height — toggle between cm and feet+inches using the mode buttons.
3
Results calculate automatically as you type. Select sex to get the correct IBW using the Devine formula.

Worked Example

Example Calculation

Patient: Female, 70 kg, 165 cm

BMI = 70 / (1.65)² = 70 / 2.7225 = 25.7 kg/m² (Overweight)

BSA (DuBois) = 0.007184 × 1650.725 × 700.425 = 1.78 m²

BSA (Mosteller) = √(165 × 70 / 3600) = √3.208 = 1.79 m²

IBW (female) = 45.5 + 2.3 × (65.0 in − 60) = 45.5 + 11.5 = 57.0 kg

About BMI and BSA in Clinical Practice

Body Mass Index (BMI) is a simple screening tool that relates weight to height squared. While it does not directly measure body fat, it is widely used to classify patients as underweight, normal weight, overweight, or obese, categories that have implications for drug dosing, surgical risk, and disease management.

Body Surface Area (BSA) is used primarily in oncology for chemotherapy dosing because it correlates more closely with cardiac output, renal clearance, and metabolic rate than weight alone. This makes BSA a better predictor of how a patient will process a cytotoxic drug. The DuBois and Mosteller formulas are both widely accepted; the choice often depends on institutional preference and the specific drug studied.

Ideal Body Weight (IBW) using the Devine formula is used for drugs that distribute primarily in lean body mass — such as aminoglycosides and certain chemotherapy agents — to avoid overdosing in obese patients. When actual weight is less than IBW, actual weight is used.

BMI Category Reference

Underweight: < 18.5 Normal: 18.5 – 24.9 Overweight: 25 – 29.9 Obese Class I: 30 – 34.9 Obese Class II: 35 – 39.9 Obese Class III: ≥ 40

Frequently Asked Questions

DuBois is the original and most widely referenced BSA formula (1916) and remains the standard in most clinical guidelines. Mosteller (1987) is simpler to calculate and equally accepted in clinical practice, including oncology dosing. Haycock (1978) was derived specifically for pediatric patients and is preferred when calculating BSA for children. In practice, the differences between formulas are small and rarely clinically significant.
BSA correlates with cardiac output, glomerular filtration rate, and metabolic rate better than body weight alone. This makes BSA a more reliable predictor of drug clearance across patients of different sizes. Using BSA reduces inter-patient variability in drug exposure, improving the balance between efficacy and toxicity. The practice was established in the 1950s and remains standard for most cytotoxic chemotherapy regimens.
Many institutions cap BSA at 2.0 m² to avoid potential overdose in very large patients, particularly because BSA-based dosing was validated in patients of average size. However, capping is controversial — some guidelines recommend against it for certain drugs, particularly in obese patients where underdosing may compromise efficacy. Always check your institution's policy and the specific drug's prescribing information.
Multiply total height in inches by 2.54. Convert feet and inches to total inches first: (feet × 12) + inches. For example, 5 feet 7 inches = 67 inches × 2.54 = 170.2 cm. This calculator accepts height in cm or feet+inches and converts automatically.
Ideal Body Weight (IBW) is used for drugs that distribute primarily in lean body mass rather than adipose tissue — such as aminoglycoside antibiotics, vancomycin, and some chemotherapy agents. Using total body weight for these drugs in obese patients would lead to overdosing. IBW is calculated using the Devine formula, which accounts for sex and height.

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