Body surface area (BSA) dosing
Some drugs use body surface area. Find the area in square meters from height and weight, and then the dose.
For practice only. Not for clinical use. The drug names and numbers are made up. Always follow your school's and your facility's rules.
Practice problem
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A patient is 40 inches tall and weighs 50 lb. Use the Mosteller formula for inches and pounds. What is the BSA, in m²?
Round to the nearest hundredth.
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How to solve it
BSA in m² equals the square root of the height in cm times the weight in kg, divided by 3,600. Dose equals the dose for each m² times the BSA.
Worked example
A patient is 148 cm tall and weighs 39.4 kg. Use the Mosteller formula. What is the body surface area (BSA), in m²?
Solution
- 148 × 39.4 = 5,831.2; ÷ 3,600 = 1.6198.
- √(148 cm × 39.4 kg ÷ 3,600) = 1.2727 m², rounded to 1.27 m².
Formula: BSA (m²) = √(height in cm × weight in kg ÷ 3,600)
Answer: 1.27 m²
Questions
Why do some drugs use body surface area?
Body surface area follows the size of the body better than weight alone. Some drugs, such as cancer drugs, use it for a more exact dose.
How do I find the BSA?
Multiply the height in cm by the weight in kg. Divide by 3,600. Then find the square root. The answer is in m².
How do I find the dose from the BSA?
Multiply the dose for each m² by the BSA. For example, 50 mg/m² for a BSA of 1.8 m² is 90 mg.
What does the rounding message mean?
Your number is right, but you did not round it as the problem asks. Round it the way the problem says. Then type it again.