Body Surface Area Calculator – BSA by Height and Weight

Drug dosing based purely on body weight has a real limitation: the human body doesn't process medications in a perfectly linear way as weight increases. For many drugs, especially chemotherapy agents, the relationship between body size and how the drug is distributed, metabolized, and cleared is better captured by surface area than by weight.

The logic goes back to physiology. Organ function, blood volume, and metabolic rate all scale more closely with body surface area than with mass alone. So when precise dosing matters, especially when too much of a drug could be seriously harmful, clinicians lean on BSA to calibrate the dose to the individual patient's size in a more meaningful way.

This is especially true in pediatrics. Children vary enormously in size, and dosing a five-year-old based on weight alone can lead to dangerous over- or underdosing. BSA-based dosing helps standardize treatment across a wide range of body sizes.

People often confuse BSA and BMI since both use height and weight, but they serve completely different purposes.

BMI is a population-level screening tool. It's quick and easy, but it says nothing about how much of your weight is fat versus muscle, and it doesn't help a doctor figure out how much medication to give you. BSA is more of a clinical measurement, tied directly to physiological calculations that affect patient care.

You can enter your measurements in either metric (centimeters and kilograms) or imperial (feet/inches and pounds) units. The calculator handles the conversion automatically, so don't worry about doing any math beforehand.

Try to use your most accurate, up-to-date measurements. BSA calculations are sensitive to the inputs, so a height that's off by a couple of inches or a weight that's significantly outdated will affect the result. If you've been weighed recently at a doctor's office, those numbers are ideal.

The calculator offers several formula options, including Du Bois, Gehan-George, Fujimoto, Boyd, and Schlich. For most people, the choice won't make a huge difference since these formulas tend to agree closely in the normal adult range. However, specific clinical contexts or institutional preferences sometimes call for a particular formula.

If you're using this for a specific medical purpose, check with your healthcare provider about which formula their practice or protocol uses. The Du Bois formula is the most common default in clinical settings, so if you're unsure, that's a reasonable starting point.

Your result will display in square meters (m²), which is the standard unit for BSA in medicine worldwide. Some calculators also show square feet (ft²) as a reference, but m² is what matters clinically.

For context, the average adult BSA falls somewhere around 1.7 to 1.9 m², though this varies by body size, age, and sex. A result that's higher or lower than that range doesn't mean something is wrong. It's simply a reflection of your body's dimensions, and it gets used as an input in other calculations rather than as a standalone diagnostic number.

If a drug dose or a clinical reference mentions "per m²," your BSA result is the number you'd multiply by to get the total dose or value for your body.

Published in 1916 by D. Du Bois and E.F. Du Bois, this formula has become the standard reference in most clinical and research settings. It was derived from measurements on just nine subjects, which is a remarkably small sample by modern standards, but it has held up well over decades of use.

The formula is: BSA = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425

It performs well for average-sized adults but can underestimate BSA in obese patients. Despite this known limitation, it remains the most commonly cited formula in drug dosing literature, largely because so many clinical studies and protocols were built around it.

Developed in 1970, the Gehan and George formula was based on a larger dataset than Du Bois, which makes it somewhat more statistically robust. It's structured similarly to the Du Bois formula but uses different exponents and a different coefficient.

The formula is: BSA = 0.0235 × Height(cm)^0.42246 × Weight(kg)^0.51456

This formula is commonly used in pediatric dosing contexts and has been validated across a broader range of body sizes. Some oncology protocols specifically reference it, so it's worth knowing if you're working through chemotherapy-related calculations.

The Fujimoto formula was developed specifically for Japanese populations and published in 1968. It recognizes that body proportions can differ across ethnic groups, and a formula calibrated to one population may not be perfectly accurate for another.

The formula is: BSA = 0.008883 × Height(cm)^0.663 × Weight(kg)^0.444

For individuals of Asian descent, particularly Japanese, this formula may yield a more accurate result than Du Bois. That said, most clinical protocols in the United States still default to Du Bois unless there's a specific reason to choose otherwise.

The Boyd formula, published in 1935, was notable for being derived from a relatively large sample and for being particularly accurate for infants and young children. It's sometimes preferred in pediatric settings where other formulas may be less reliable at very small body sizes.

Boyd: BSA = 0.0003207 × Height(cm)^0.3 × Weight(g)^(0.7285 - 0.0188 × log(Weight(g)))

The Schlich formula, developed more recently, takes a different approach by using separate equations for men and women, acknowledging that body composition differences between sexes can affect surface area estimation.

Schlich (women): BSA = 0.000975482 × Height(cm)^1.8 × Weight(kg)^0.5
Schlich (men): BSA = 0.000579479 × Height(cm)^1.24 × Weight(kg)^0.38

These formulas aren't as widely used in everyday clinical practice, but they're valuable in research and in situations where precision across different populations is a priority.

Honestly, for most purposes, the formula you choose won't dramatically change your result if you're an average-sized adult. The formulas tend to agree within a few percent of each other in the normal range.

That said, here's a practical guide:

• General use or unknown context: Du Bois is the safe default.
• Pediatric patients: Gehan-George or Boyd tends to be more reliable.
• Patients of Asian descent: Fujimoto may be more accurate.
• When sex-specific accuracy matters: Schlich is worth considering.
• Following a clinical protocol: Use whatever formula that protocol specifies.

When in doubt, ask your healthcare provider which formula their institution uses for the relevant calculation. Consistency within a protocol matters more than which formula is theoretically best.

Newborns have a remarkably small BSA, around 0.25 m², but relative to their body weight, they actually have a much higher surface-area-to-mass ratio than adults. This has real implications for how they handle heat loss, fluid balance, and drug metabolism.

As children grow, BSA increases steadily. The jump during adolescence is particularly significant because growth spurts rapidly change height and weight together. This is one reason pediatric drug dosing requires careful, individualized calculation rather than a simple age-based rule.

Adult BSA varies based on height, weight, and sex. The commonly cited "standard" BSA of 1.73 m² (used in some clinical formulas as a reference value) was derived from older research and represents an idealized average, not a goal or a normal range. Your actual BSA is simply what it is based on your body's dimensions.

This is probably the most well-known application. Most chemotherapy drugs are dosed in milligrams per square meter (mg/m²). The oncologist calculates your BSA and then multiplies it by the protocol-specified dose to get the total amount you'll receive.

The rationale is that BSA correlates better than weight with drug clearance, toxicity thresholds, and therapeutic response for many cytotoxic agents. Getting this right matters enormously because the margin between an effective dose and a toxic one can be narrow with chemotherapy.

It's worth noting that BSA-based dosing isn't perfect, and there's ongoing research into whether pharmacokinetic monitoring (actually measuring drug levels in the blood) might eventually replace or supplement BSA-based approaches for some drugs. But for now, BSA remains the clinical standard for most chemotherapy protocols.

Cardiac output measures how much blood the heart pumps per minute. The problem is that a healthy cardiac output for a large person would be inadequate for a small person. To make the measurement meaningful across different body sizes, clinicians divide cardiac output by BSA to get the cardiac index.

Cardiac Index = Cardiac Output (L/min) ÷ BSA (m²)

A normal cardiac index is roughly 2.5 to 4.0 L/min/m². Values outside this range can signal heart failure, cardiogenic shock, or hyperdynamic states like sepsis. BSA adjustment is what makes this comparison valid across patients of different sizes, so a reading that looks fine in one patient isn't misinterpreted in another.

Glomerular filtration rate (GFR) measures how well the kidneys are filtering blood. Raw GFR values depend heavily on body size, which makes comparisons between patients difficult without some kind of normalization.

The standard approach is to express GFR adjusted to a BSA of 1.73 m², written as mL/min/1.73 m². This is what you see reported on most lab results as eGFR (estimated GFR). The 1.73 m² figure comes from an older reference standard representing average adult BSA, and while it has its critics, it remains the universal convention in nephrology.

This adjustment matters clinically because it allows doctors to compare kidney function results across patients of very different sizes and to use standardized cutoffs for chronic kidney disease staging. Without BSA normalization, a small elderly woman and a large young man with the same underlying kidney function could have very different raw GFR numbers, which would complicate diagnosis and treatment decisions considerably.