Calculate Body Surface Area (BSA) for medication dosing using the Mosteller or Haycock (pediatric) formula.
📖 Mosteller / Haycock EquationsFill in the fields on the left with your information, then press Calculate to see your result instantly. No sign-up required, and no data is sent anywhere — everything is calculated right in your browser.
Body Surface Area (BSA) is used in medicine mainly to calculate the dosage of certain medications — especially chemotherapy agents and some heart and kidney medications — more precisely than relying on body weight alone, since surface area correlates more closely with metabolic rate, blood volume, and organ size than weight does. This calculator offers two formulas built from height and weight: the Mosteller equation (BSA = √(height × weight / 3600)), the most common and widely used for adults thanks to its simplicity and good accuracy across body sizes, and the Haycock equation, which is specifically validated for children and infants because their body proportions differ from adults. Both formulas were derived by comparing predicted values against directly measured body surface area in clinical studies. The result here is purely educational; any real medication dosage must always be calculated and confirmed by a qualified physician or pharmacist.
Most drug doses are calculated per kilogram of body weight, but for a specific and clinically important group of medications — chemotherapy drugs being the clearest example — dosing by weight alone can under- or over-treat patients of different body shapes. Body Surface Area (BSA) was adopted decades ago as a better proxy, because it correlates more closely with blood volume, cardiac output, and metabolic rate than weight does on its own, particularly for drugs with a narrow safety margin between an effective dose and a toxic one.
The most widely used formula today is the Mosteller equation, published in 1987, which calculates BSA as the square root of (height in cm × weight in kg, divided by 3600). Its appeal is simplicity combined with accuracy that holds up well across the adult population, which is why it has become the default in most adult oncology dosing protocols. An older and more complex alternative, the Du Bois formula from 1916, is still referenced in some literature but has largely been superseded by Mosteller's simpler calculation.
Children present a different challenge: their body proportions — the ratio of surface area to weight — differ substantially from adults, particularly in infancy. The Haycock equation, developed and validated specifically in pediatric populations, accounts for this and is generally preferred for infants and young children rather than applying an adult-derived formula to a body shape it wasn't built for.
In practice, BSA-based dosing shows up most in chemotherapy, where doses are typically expressed in milligrams per square meter of body surface rather than per kilogram, and in select cardiac and renal medications where the same logic applies. A calculated BSA of around 1.7 m² is often used as a rough population reference point for an average adult, though any individual's actual value can vary meaningfully based on height and weight.
It's worth being clear about what this calculator does and doesn't do: it applies a validated formula to the numbers you provide, but it cannot account for a patient's kidney or liver function, other medications, or the specific dosing protocol a treating physician is following. Any real prescription decision — especially involving chemotherapy — must be calculated, cross-checked, and confirmed by a qualified physician or pharmacist using the patient's complete clinical picture.
BSA reflects overall body size and metabolic rate more accurately than weight alone, which is important for drugs with a narrow safety margin like chemotherapy.
Haycock is generally recommended for infants and children, since it was specifically validated for pediatric body proportions.
No. Always let a physician or pharmacist calculate and confirm any actual medication dose.