Body Surface Area Calculator · Practical guide
The Mosteller Formula for BSA
One square root, two measurements — the simplest validated way to estimate body surface area.
At a glance
The Formula
The Mosteller formula, published in the New England Journal of Medicine in 1987, estimates body surface area as:
BSA (m²) = √( height(cm) × weight(kg) ÷ 3600 )
That is the entire calculation — square root of height times weight divided by 3600. Its simplicity is why it became the most commonly used BSA equation in clinical practice, and it is one of the four formulas this calculator computes side by side.
Interactive tool
Body Surface Area Calculator
Enter your own values, then compare the result with the examples below.
Body Surface Area Results
A Worked Example
For a person who is 175 cm tall and weighs 70 kg: 175 × 70 = 12,250; 12,250 ÷ 3600 ≈ 3.4028; and √3.4028 ≈ 1.845 m². For comparison, the same inputs give 1.848 m² by Du Bois, 1.847 m² by Haycock, and 1.851 m² by Boyd — the formulas agree within a fraction of a percent.
Mosteller in Imperial Units
The same equation works in pounds and inches with a different divisor: BSA = √( height(in) × weight(lb) ÷ 3131 ). Someone who is 67 inches and 154 pounds gets √(67 × 154 ÷ 3131) = √3.2957 ≈ 1.82 m². The calculator converts units automatically, so you can enter either system.
Why Clinicians Prefer It
Because it needs only a square root, the Mosteller formula can be computed at the bedside without a scientific calculator or lookup chart, which reduces arithmetic errors on weight-based and BSA-based drug orders. Studies comparing the major equations show Mosteller tracks the classic Du Bois result closely across both adults and children, which is why it is the default in many dosing references.
Frequently Asked Questions
Is the Mosteller formula accurate for children?
Yes, it is validated for pediatric use and widely used in children's hospitals. Some clinicians still prefer Haycock or Boyd for infants, which is why this calculator shows all four results together.
What is the 3600 in the Mosteller formula?
It is a scaling constant chosen so the equation reproduces measured body surface areas when height is in centimeters and weight is in kilograms. With imperial units the divisor becomes 3131 instead.
Do I use actual or ideal body weight in the Mosteller formula?
BSA equations are defined on actual measured weight. Some clinical protocols adjust dosing weight for very obese patients, but that adjustment happens after BSA is computed — follow the specific protocol.
How do I convert BSA back to a drug dose?
Multiply the drug's prescribed dose per square meter by the BSA value. For example, 100 mg per m² with a BSA of 1.85 m² gives a dose of 185 mg.