Body Surface Area (BSA) Calculator
Get BSA in m² from height and weight using Mosteller or Du Bois
Body surface area, formulas and use-case FAQ
What does this BSA calculator give me?
It calculates body surface area in m² from height and weight. You will see a value from the Mosteller formula and one from Du Bois so you can match what your guidelines reference.
Which formula should I use: Mosteller or Du Bois?
Many modern tools and protocols use Mosteller because it is simple and performs well in practice. Du Bois is an older, widely cited equation. When in doubt, follow whichever formula your local protocol, calculator or order set specifies.
Why is BSA used instead of just body weight?
Some medications and clinical indexes scale better with surface area than with weight alone. BSA partly reflects body size in two dimensions and has been traditional for chemotherapy and some other drugs, although there is ongoing debate about its limitations.
What is a typical BSA for adults?
Many adults fall around 1.6–1.9 m², but smaller or larger people can sit outside that range. Children and very small or very large adults can have BSA values well below or above those numbers.
Does this replace my hospital’s dosing tools?
No. This page is a standalone helper. For real prescribing and administration, use the BSA calculator, order set or protocol built into your clinical system so dosing rules, caps and warnings are all applied.
Can small changes in height or weight matter?
Yes, especially near protocol cut-offs. Measure height and weight carefully and re-check BSA when weight changes meaningfully or when paediatric patients are growing quickly.
Is BSA useful outside of medication dosing?
BSA also appears in formulas such as cardiac index and glomerular filtration rate indexes, where values are normalised per square metre of body surface area.
Who should double-check results most carefully?
Anyone using BSA for drug dosing, high-risk therapies or critical care decisions should treat this tool as a quick cross-check only and verify numbers with official calculators and pharmacy or medical staff.
How to use this BSA calculator in practice
This calculator turns a simple height and weight pair into a body surface area value in square metres (m²). It is designed so you can quickly match or sanity-check the BSA used in chemotherapy protocols, drug-dosing tables or indexed clinical values without opening a spreadsheet.
1. Choose units and formula
Start with the units you measure in most often. The tool loads in US units so you can enter height in feet and inches and weight in pounds. If you prefer centimetres and kilograms, switch to metric. Then confirm the formula: Mosteller is the default, with Du Bois as the classic alternative.
2. Enter height and weight
In US mode, type height as feet plus inches and weight in lb. In metric mode, enter height in cm and weight in kg. Use current, measured values where possible. The calculator converts behind the scenes so both formulas receive the correct inputs.
3. Read the BSA in m²
Tap Calculate BSA in m². You will see:
- A highlighted BSA based on your chosen formula (Mosteller or Du Bois).
- A second BSA from the other formula for quick comparison.
- A short note on how the result fits within common adult ranges.
If your local system uses one specific equation, match that value and treat the other as a cross-check.
4. Copy the summary into your notes or chart
Use Copy summary to paste height, weight and the BSA outputs into notes, handover templates or learning materials. That way you can show how the value was derived without repeating the calculation.
5. Combine BSA with local protocols
For any real-world dosing, follow institutional guidelines and product information. Many protocols also use caps, rounding rules or adjustments for organ function that a simple BSA calculator does not apply. Treat this page as a quick, transparent math helper rather than a full prescribing tool.
If you are a patient or caregiver looking at BSA out of curiosity, avoid changing doses or treatments on your own. Instead, use the number as a talking point with your clinical team so decisions stay aligned with your overall care plan.
How the BSA math works
Both Mosteller and Du Bois use the same two inputs — height and weight — to estimate body surface area. The main difference is how they combine those inputs mathematically.
1. Converting units
No matter which unit mode you choose, the calculator converts values to centimetres and kilograms before applying the formulas. Feet and inches become centimetres, and pounds become kilograms, so the equations match their original definitions.
2. Mosteller formula
The Mosteller equation is a simplified square-root method that many modern calculators and hospital tools adopt:
BSA (m²) = √[ height(cm) × weight(kg) ÷ 3600 ]
It balances ease of use with reasonable agreement to more complex formulas in typical clinical populations.
3. Du Bois formula
The Du Bois and Du Bois equation is older and slightly more complex, using exponents on height and weight:
BSA (m²) = 0.007184 × height(cm)0.725 × weight(kg)0.425
This formula has a long history in research and dosing tables, which is why many references still mention it alongside or instead of newer methods.
4. Typical ranges and rounding
For adults, BSA values often cluster around 1.7 m² with common ranges roughly between 1.5–2.3 m² depending on body size. The calculator rounds to two decimal places so the result is easy to read and copy into notes, while still being precise enough for most conceptual and educational uses.
For any situation where BSA feeds into high-risk dosing or critical decisions, always use your official clinical calculator or electronic health record tools as the source of truth.
References and further reading on body surface area formulas
These references explain the Mosteller and Du Bois equations and discuss how BSA is used clinically:
- StatPearls — Body Surface Area — reviews common BSA formulas, including Du Bois and Mosteller, and outlines clinical uses and limitations.
- GlobalRPH — Body Surface Area (BSA) Calculator — lists several BSA equations and highlights the simplified Mosteller formula widely used in practice.
- Medschool.co — Body Surface Area — shows the Du Bois equation, the Mosteller method and supporting references for both.
Use these as background reading and rely on your institution’s protocols and tools for real-world dosing and clinical decisions.