Body Surface Area Calculator · Practical guide
BSA for Chemotherapy Dosing
Why chemo doses are written in mg per m², and how to turn your height and weight into the BSA behind them.
At a glance
Why Chemo Is Dosed by BSA
Body surface area correlates more closely with blood volume, cardiac output, and kidney function than weight alone. Because chemotherapy drugs have narrow safety margins, oncologists prescribe most of them in milligrams per square meter (mg/m²) so the dose scales with each patient's body size rather than giving every adult the same flat amount.
Interactive tool
Body Surface Area Calculator
Enter your own values, then compare the result with the examples below.
Body Surface Area Results
A Worked Dosing Example
Suppose a protocol calls for 100 mg/m². A patient who is 175 cm and 70 kg has a BSA of about 1.85 m² (Mosteller: √(175 × 70 ÷ 3600) ≈ 1.845). The dose is 100 × 1.845 ≈ 185 mg. A taller or heavier patient at 180 cm and 80 kg has a BSA of about 2.00 m², and the same protocol yields 200 mg — the per-m² rule scales the dose automatically.
Which Formula Do Oncology Teams Use?
Du Bois is the historical standard, while Mosteller has become the everyday favorite because it is simple enough to double-check by hand. Most institutions standardize on one equation and stick with it. In practice the major formulas differ by only 1 to 2 percent for typical adults — the worked example above gives 1.845 (Mosteller), 1.848 (Du Bois), 1.847 (Haycock), and 1.851 (Boyd) for the same patient.
Important Limitations
BSA-based dosing is a starting point, not the whole decision. Oncologists adjust for kidney and liver function, blood counts, prior treatment, and sometimes cap doses in very obese patients. Never adjust a chemotherapy dose on your own — this page explains the math so the numbers on your treatment plan make sense; the dose itself belongs to your oncology team.
Frequently Asked Questions
Why not just dose chemotherapy by body weight?
Weight includes fat tissue, which metabolizes many drugs poorly. BSA tracks metabolic capacity and organ perfusion better, so it produces more consistent drug exposure across differently built patients.
What is a typical adult BSA for chemo calculations?
The average adult man measures about 1.9 m² and the average adult woman about 1.6 m², though individual values vary widely with height and weight.
Do all chemotherapy drugs use BSA dosing?
No. Some newer agents use flat dosing or weight-based dosing, and a few use AUC-based methods like the Calvert formula for carboplatin. Your team follows the protocol specific to each drug.
How often is BSA recalculated during treatment?
Usually at the start of each cycle or whenever weight changes significantly — often a threshold of about 5 to 10 percent. Keeping height and weight current keeps the dose accurate.