BSA-Based Dosage Calculator
Calculates medication dose using body surface area (BSA) derived from the Mosteller formula applied to weight and height. Essential for chemotherapy and other drugs where BSA-based dosing improves safety and efficacy.
About this calculator
Body surface area (BSA) is used instead of body weight for drugs whose distribution and clearance correlate more closely with the body's total surface than its mass — most notably chemotherapy agents. BSA is calculated using the DuBois formula: BSA (m²) = 0.007184 × weight(kg)^0.425 × height(cm)^0.725. Once BSA is known, the total dose is: Total Dose (mg) = BSA (m²) × Dose per m² (mg/m²). The DuBois formula has been validated extensively since 1916 and remains a clinical standard alongside the Mosteller and Haycock formulas. BSA-based dosing helps account for body size differences across patients while reducing the risk of under- or over-dosing toxic agents. The result should always be reviewed against protocol-specified dose caps.
How to use
A patient weighs 70 kg and is 175 cm tall, prescribed a drug at 100 mg/m². Step 1 — calculate BSA: BSA = 0.007184 × (70^0.425) × (175^0.725). First, 70^0.425 ≈ 6.107 and 175^0.725 ≈ 38.44. Then BSA = 0.007184 × 6.107 × 38.44 ≈ 0.007184 × 234.7 ≈ 1.687 m². Step 2 — calculate dose: 1.687 m² × 100 mg/m² = 168.7 mg. The patient should receive approximately 169 mg, subject to protocol maximum dose review.
Frequently asked questions
Why is body surface area used instead of body weight for chemotherapy dosing?
Chemotherapy drugs have very narrow therapeutic windows — too little is ineffective, too much is toxic. Research dating back to the 1950s showed that many pharmacokinetic parameters, such as drug clearance by the kidneys and liver, correlate better with BSA than with body weight alone. BSA integrates both weight and height, giving a more complete picture of the body's metabolic capacity. While BSA-based dosing is not perfect — studies show it does not eliminate inter-patient variability in drug exposure — it remains the standard practice for most oncology protocols.
What is the DuBois formula and how does it calculate body surface area?
The DuBois formula, published in 1916 by Delafield DuBois and Eugene DuBois, estimates BSA as: BSA = 0.007184 × weight(kg)^0.425 × height(cm)^0.725. It was derived from direct surface measurements of nine subjects and has since been validated in larger populations. The formula produces BSA in square meters and is one of several validated equations — others include Mosteller (BSA = √(height × weight / 3600)) and Haycock. Different institutions may use different formulas, which can lead to small differences in calculated dose, so it is important to know which formula your clinical protocol specifies.
How do I know if a medication should be dosed by BSA or by body weight?
Drug prescribing information and clinical treatment protocols specify which dosing method to use. BSA-based dosing is most common for cytotoxic chemotherapy, certain immunosuppressants, and some antifungals. Weight-based dosing (mg/kg) is more common for antibiotics, anticoagulants, and many pediatric medications. If the prescribed dose is listed as mg/m², use BSA dosing. When in doubt, consult the drug's summary of product characteristics (SPC) or a clinical pharmacist, as using the wrong method can result in significant dosing errors for high-risk medications.