Body Surface Area (BSA) Calculator
The gold standard for medical calculations. Accurately estimate the total surface area of the human body for precise drug dosing, metabolic assessments, and cardiac index.
5 Formulas
Mosteller, Du Bois +
Dosage
Chemo & Pediatrics
Cardiac Index
Heart performance
Kidney GFR
Renal function
What is Body Surface Area?
BSA is the measured or calculated surface area of a human body. It is considered the most reliable indicator of metabolic mass, far superior to simple body weight.
Why Weight Isn't Enough
In medicine, dosing drugs by weight alone (e.g., mg/kg) can be dangerous for obese or very thin patients because fat tissue does not metabolize drugs the same way lean tissue does. BSA provides a more accurate normalization for metabolic rate.
Oncology (Chemotherapy)
Cytotoxic drugs have a narrow therapeutic index. BSA dosing minimizes toxicity while maximizing efficacy.
Cardiology
Used to calculate Cardiac Index (Cardiac Output / BSA), which assesses heart performance relative to body size.
Nephrology
Essential for Glomerular Filtration Rate (GFR) calculations to assess kidney function.
Mosteller Formula
The simplest and most widely used formula in modern medicine for routine clinical use.
Du Bois Formula
The classic standard (1916), still widely used for obesity research and precise metabolic studies.
Haycock Formula
Specifically optimized for pediatrics, providing better accuracy for infants and children.
Why Choose Our Tool?
Multi-Formula Comparison
We calculate using 5 different formulas simultaneously so you can compare results and find the consensus.
Universal Units
Seamlessly switch between Metric (cm/kg) and Imperial (ft/lb) without manual conversion errors.
Reference Ranges
We provide standard BSA values for different age groups to help contextuaize your result.
How to Use the BSA Calculator
Accurate results in 2 steps.
Choose Unit System
Select "Metric" for centimeters and kilograms, or "Imperial" for feet/inches and pounds.
Enter Measurements
Input height and weight. Click calculate. You will see results for all major medical formulas instantly.
Calculate Your BSA
Enter patient stats below.
Understanding BSA Values
What is "Normal"? Reference values vary by age and gender.
Understanding Your BSA Value
A BSA of 1.73 m² is considered the "average" for adults. But variances matter clinically.
The "Standard" (1.73 m²)
Most kidney function tests (GFR) and drug dosages are normalized to a standard adult surface area of 1.73 m². If your BSA is significantly higher or lower, standard doses may need adjustment.
High BSA (> 2.0 m²)
Indicates a larger metabolic mass. In chemotherapy, this might require a higher dose to be effective. In cardiology, a "normal" cardiac output might actually be insufficient for a body of this size.
Low BSA (< 1.6 m²)
Common in small adults or children. Using standard adult doses on a low BSA patient carries a high risk of toxicity or overdose. Precision is critical here.
The Formulas
Mosteller is the most common, but others have specific uses.
Mosteller (1987)
sqrt( (H x W) / 3600 )
Simplified calculation. Easy to memorize and use in clinical rounds.
Du Bois (1916)
0.007184 × W^0.425 × H^0.725
The historical benchmark. Still required by some older protocols.
Haycock (1978)
0.024265 × W^0.5378 × H^0.3964
Validated for infants and children, making it preferred in pediatrics.
Gehan & George (1970)
0.0235 × W^0.51456 × H^0.42246
Often used for cancer chemotherapy dosing.
Applications of BSA
Chemotherapy Dosing
Chemo drugs have a narrow safety margin. Dosing by BSA normalizes metabolic rate better than weight alone, reducing toxicity risks.
Cardiac Index
Cardiac Output divided by BSA gives the Cardiac Index. This tells doctors if the heart is pumping enough blood *for the size of the person*.
Pediatrics
Children's metabolism varies wildly with size. BSA provides a smoother curve for calculating fluid and electrolyte needs than weight alone.
Why is BSA Critical for Healthcare?
Using weight alone is often inaccurate. BSA provides a better estimate of metabolic mass.
Metabolic Scaling
Metabolic rate doesn't scale linearly with weight. A person who weighs twice as much doesn't have double the metabolism. BSA scales roughly to the 2/3 power of weight, which matches metabolic heat production much more closely.
This means BSA is the most scientifically accurate way to compare physiological parameters (like blood volume or kidney filtration) between people of vastly different sizes.
Preventing Toxicity
For drugs with a "narrow therapeutic index" (where the difference between a cure and a poison is small), accuracy is life or death.
If a doctor prescribed chemotherapy based solely on weight for an obese patient, the dose might be lethally high. BSA corrects for excess adipose tissue (fat), which doesn't metabolize the drug, ensuring a safer dose.
Pro Tips for Accuracy
Height Matters
Even a small error in height can skew BSA significantly. Always measure height without shoes, heels against the wall.
Amputees
Standard BSA formulas are invalid for amputees. Specialized adjustments must be made to account for missing limb surface area.
Fluid Status
Use "Dry Weight" for patients with significant edema (water retention). Using fluid-overloaded weight will overestimate BSA.
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Frequently Asked Questions
Why are there so many formulas?
Each formula was developed based on different patient populations (e.g., infants vs adults). The Mosteller formula is now the most common because it is mathematically simpler but just as accurate.
Is BSA better than BMI?
They have different uses. BMI is for obesity screening. BSA is for metabolic dosing. BSA is more accurate for determining blood volume and metabolic rate.
Why calculate BSA for adults?
Standard adult drug doses assume a "normal" sized adult (1.73 m²). If a patient is very large or small, standard doses can be toxic or ineffective. BSA allows for adjustment.
Which formula should I use?
For general purposes, Mosteller is recommended. For pediatrics, Haycock is preferred. Always follow your institution's specific protocol for clinical decisions.