Body Surface
Area Calculator
Calculate your Body Surface Area (BSA). BSA is used in clinical settings and to determine metabolic rates more accurately than BMI.
What Is Body Surface Area?
Body Surface Area (BSA) is the measured or calculated surface area of a human body. For many clinical purposes, BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose tissue.
The Mosteller Formula
This calculator uses the Mosteller formula, which is the most widely used and accepted formula for BSA calculation due to its simplicity and accuracy. The formula is: BSA = √((Height × Weight) / 3600).
Using the estimate well
Understanding Your Body Surface Area Result
Body surface area, or BSA, is an estimate of the body’s external surface expressed in square metres. It is used in some clinical calculations because it scales body size differently from weight alone. Budget Meal Planning applies the same idea to meal planning.
Online calculators simplify real life into a small number of inputs. Use this result as a transparent estimate that you can review, not as proof that a particular outcome will occur.
Enter consistent information
Enter a recent height and weight using matching units. The calculator applies a published equation, but different BSA equations can return slightly different values, particularly at very small or very large body sizes.
Before saving the answer, check the units, decimal points and assumptions shown by the tool. If you compare results later, use the same method so the trend is meaningful. Budget Meal Planning for a Family of 5 applies the same idea to meal planning.
Interpret the number in context
A BSA number is not a health score and has no stand-alone ‘good’ range. Clinicians may use it when considering medication dosing, cardiac measurements or other body-size adjustments, together with the patient’s diagnosis and laboratory information.
Never change a prescription or treatment dose from an online BSA result. Paediatric care, cancer treatment, kidney or liver impairment and unusual body composition all require clinician-led calculation and judgement.
A practical next step
Use the result to understand a calculation already discussed with your care team. If the number differs from a medical record, check the units and equation before drawing conclusions.
- Save the inputs with the date instead of recording only the final number.
- Look for a repeatable trend and avoid reacting to one unusually high or low result.
- Use qualified medical or coaching support when the decision affects health, treatment or safety.
Common questions
Is the result exact? No. It is the output of the displayed formula and the information entered. Measurement error and individual variation still apply.
How often should it be recalculated? Recalculate when the underlying inputs meaningfully change. Repeating it several times a day usually adds noise rather than useful information.
Can it replace professional advice? No. It is an educational planning aid and cannot assess symptoms, diagnose a condition or account for a complete personal history.