BSA Calculator (Body Surface Area)
Enter height and weight, choose your preferred formula, and calculate Body Surface Area (BSA) instantly.
Educational tool only. Clinical decisions should always be made by qualified professionals using official protocols.
What Is BSA and Why Do We Calculate It?
BSA stands for Body Surface Area, an estimate of the total external surface of the human body. It is usually expressed in square meters (m2). In healthcare, BSA is often used because many physiological processes and treatment plans correlate better with body surface area than with body weight alone.
The most common reasons people look up a calculation for BSA include:
- Medication dosing, especially in oncology and specialized therapies.
- Estimating renal function and cardiac index in clinical settings.
- Pediatric assessments where growth and body proportions vary widely by age.
- Research and epidemiology where standardization by body size is needed.
Common BSA Formulas
There is no single universal formula. Different equations were developed from different study groups and can produce slightly different values. The calculator above includes four widely recognized formulas:
1) Mosteller Formula
BSA = √((height in cm × weight in kg) / 3600)
Mosteller is popular because it is simple and generally close to other standard methods. In many practical settings, this is the default.
2) Du Bois & Du Bois Formula
BSA = 0.007184 × height(cm)0.725 × weight(kg)0.425
This is one of the earliest and most historically cited BSA formulas. It remains important in literature and clinical references.
3) Haycock Formula
BSA = 0.024265 × height(cm)0.3964 × weight(kg)0.5378
Haycock is often discussed in pediatric contexts because it was designed to improve fit across a broad range of body sizes.
4) Gehan & George Formula
BSA = 0.0235 × height(cm)0.42246 × weight(kg)0.51456
Another validated approach that may differ slightly from Mosteller or Du Bois in certain body compositions.
How to Do a Manual Calculation for BSA
If you want to verify a value manually, here is a quick Mosteller example:
- Height = 170 cm
- Weight = 70 kg
- Multiply: 170 × 70 = 11,900
- Divide: 11,900 / 3600 = 3.3056
- Square root: √3.3056 = 1.818
So the estimated BSA is approximately 1.82 m2.
Metric vs Imperial Inputs
BSA equations are typically based on metric units (cm and kg). When imperial values are used, they are converted first:
- inches to centimeters: cm = in × 2.54
- pounds to kilograms: kg = lb × 0.45359237
This calculator handles those conversions automatically when you select the Imperial option.
Interpreting BSA Results
A BSA value by itself is not a diagnosis. It is a size-adjustment metric. In adults, many values often fall roughly in the 1.5 to 2.3 m2 range, but normal varies by height, weight, age, and body composition.
Important points:
- Different formulas can produce small differences.
- Clinical teams may require one specific formula for consistency.
- Special populations (pediatric, obesity, cachexia) may require extra interpretation.
- BSA should be considered alongside labs, history, and medical judgement.
Practical Tips for Accurate BSA Calculation
Use reliable measurements
Height and weight errors directly affect BSA. Use recent measurements, remove shoes for height, and use calibrated scales when possible.
Match the formula to the context
If your institution or protocol uses Mosteller, stick with it for comparisons over time. Formula switching can create small but confusing differences.
Document units and formula
Whenever BSA is used in records, note both the formula and units. This improves reproducibility and prevents dosing errors.
Frequently Asked Questions
Is BMI the same as BSA?
No. BMI estimates body mass relative to height, while BSA estimates body surface. They serve different clinical and research purposes.
Which BSA formula is best?
There is no absolute best for every scenario. Mosteller is popular for simplicity; Du Bois is historically significant; Haycock and Gehan & George may be preferred in specific populations or institutional protocols.
Can I use this calculator for drug dosing?
Use it as an educational reference. For actual dosing, always follow licensed clinician guidance, formal treatment protocols, and pharmacy verification.
Bottom Line
A proper calculation for BSA is straightforward when height and weight are accurate and the formula is clear. The calculator on this page gives you fast results in both m2 and ft2, with support for metric and imperial units. For clinical use, always pair numerical output with professional judgement.