🩺 Clinically-Referenced BSA Guidance · Updated January 2026 · Free
Body Surface Area Calculator — Free BSA Calculator
Use our free body surface area calculator to estimate your BSA in square metres from height and weight, using the Mosteller, DuBois or Haycock formula. This BSA calculator is built for quick, accurate reference and clear clinical context.
Small Frame <1.6 m²
Average Adult 1.6–2.0 m²
Larger Frame 2.0–2.3 m²
Very Large 2.3+ m²
📅 Last Updated: January 2026🩺 Reviewed by NHS-Aligned Health Review Panel✅ Core Web Vitals Friendly🆓 Free · No Sign-Up
✍️
Written byBMI Calculator NHS Editorial TeamEditorial team covering body measurement calculators and UK public-health guidance
🩺
Medically ReviewedNHS-Aligned Health Review PanelReviewed against published BSA formula literature and clinical dosing references
What Is a Body Surface Area Calculator?
A body surface area calculator estimates the total surface area of a person's skin, expressed in square metres (m²), using their height and weight. Unlike BMI, which screens for weight status, body surface area is mainly used as a scaling tool in clinical settings — most notably for calculating chemotherapy doses, assessing burns, and estimating fluid or medication requirements in both adults and children.
This BSA calculator lets you enter your height and weight, choose from the three most recognised formulas, and get an instant result along with plain-English interpretation. It's designed for general reference, students, carers and anyone curious about how BSA is calculated — not as a substitute for a clinician's dosing calculation.
Key Takeaways
✅ A body surface area calculator estimates skin surface area in m² from height and weight.
✅ The Mosteller formula is the most widely used BSA calculator method in modern clinical practice.
✅ Average adult BSA is roughly 1.7–2.0 m², varying by height, weight and build.
✅ BSA is central to chemotherapy dosing, burns assessment and some paediatric drug calculations.
✅ This tool is for general information only — never adjust real medication doses without a clinician.
Featured snippet summary: Body surface area (BSA) is calculated from height and weight using formulas such as Mosteller: BSA (m²) = √(height in cm × weight in kg ÷ 3600). The average adult BSA is approximately 1.7 to 2.0 square metres.
How to Use This BSA Calculator
Choose metric or imperial units in the calculator on the right.
Enter your height and weight accurately.
Select which formula to use — Mosteller (default), DuBois, or Haycock.
Select "Calculate BSA" to see your instant result in m².
Read the interpretation section to understand what the figure typically represents.
If you're more interested in weight-based screening rather than clinical surface area, our BMI Calculator NHS and ideal weight calculator UK may be more relevant starting points.
Body Surface Area Formula: Mosteller, DuBois and Haycock
The Mosteller formula is the simplest and most widely used method for calculating body surface area in modern clinical practice, largely because it's easy to compute and produces results very close to more complex historical formulas.
DuBois and DuBois formula
BSA (m²) = 0.007184 × height (cm)0.725 × weight (kg)0.425. Published in 1916, this was the original reference formula used in medicine for decades and remains a recognised benchmark.
Haycock formula
BSA (m²) = 0.024265 × height (cm)0.3964 × weight (kg)0.5378. Developed in 1978, the Haycock formula is often preferred for infants and small children because it was validated across a wide paediatric weight range.
Worked example
Height 170cm, Weight 70kg (Mosteller): 170 × 70 = 11,900 → 11,900 ÷ 3600 = 3.306 → √3.306 = 1.82 m², a typical result for an average-height, average-weight adult.
There's no single "correct" BSA — unlike BMI, it isn't used to classify someone as underweight or overweight. Instead, BSA scales with body size and is used as a reference point for dosing and physiological calculations. The table below shows typical adult BSA ranges for context only.
Group
Typical BSA
Notes
Newborn infant
≈0.25 m²
BSA-based dosing is common in neonatal care
Child (5–10 years)
≈0.7–1.1 m²
Haycock formula often preferred
Adolescent
≈1.3–1.7 m²
Approaches adult range
Average adult
1.7–2.0 m²
Most common range for adult men and women
Larger-framed adult
2.0–2.3 m²
Taller or higher-weight individuals
Very large adult
2.3 m²+
Less common; clinical dosing caps sometimes applied
Quick answer: what is a normal BSA for an adult?
An average adult body surface area is roughly 1.7 to 2.0 square metres. This varies naturally with height, weight and body composition, and is not itself a marker of good or poor health — it is simply a scaling measurement.
Clinical Uses of Body Surface Area
Chemotherapy and medication dosing
Many chemotherapy drugs and some other medications are dosed in milligrams per square metre (mg/m²) rather than per kilogram, because BSA correlates more closely with metabolic rate, cardiac output and kidney function than body weight alone. This helps produce more consistent dosing across patients of different sizes.
Burns assessment
BSA is also used to estimate the percentage of a person's body affected by burns, which guides fluid resuscitation and treatment planning in emergency and burns units.
Paediatric medicine
Because children's body proportions differ significantly from adults, BSA-based dosing is common in paediatrics, where formulas like Haycock are often favoured for their validation across lower weight ranges.
Important: BSA-based drug dosing must always be calculated and verified by a qualified doctor or pharmacist. This calculator is for general educational purposes only and must never be used to determine or adjust real medication doses.
Interpreting Your BSA Result
Once you've used the calculator, your result simply reflects your estimated surface area based on the formula selected. There is no "healthy" or "unhealthy" BSA category in the way there is for BMI — instead, consider:
Consistency across formulas: Mosteller, DuBois and Haycock usually produce results within a few hundredths of a square metre of each other for adults.
Clinical context: if you were given this calculator by a healthcare provider, always confirm the exact figure and formula they intend to use, since small formula differences can matter in precise dosing.
General reference only: for everyday health tracking, BMI, waist-to-height ratio or body fat percentage are usually more relevant than BSA.
Common mistakes when using a BSA calculator
Entering height in the wrong unit (cm vs m) — always double check before calculating.
Assuming BSA is a health "score" — it is a size reference, not a wellness indicator.
Using an adult formula without validation for very young infants.
Relying on an online calculator for real medication dosing instead of a clinician's calculation.
BSA Formula Comparison Table
Formula
Published
Best suited for
Complexity
Mosteller
1987
General adult and paediatric use
Simple, square-root based
DuBois & DuBois
1916
Historical clinical reference
Moderate, power-based
Haycock
1978
Infants and small children
Moderate, power-based
Real life example
Consider two adults: one at 160cm and 55kg, the other at 190cm and 95kg. Using the Mosteller formula, the first has a BSA of approximately 1.56 m², while the second has a BSA of approximately 2.24 m² — nearly 0.7 m² more surface area, illustrating how much height and weight combined can influence the result.
Expert tips
Use the same formula consistently if tracking BSA over time, since results vary slightly between methods.
Record height and weight accurately and recently, as BSA changes with body composition changes.
If a clinician has requested a BSA figure, always confirm which formula they use for their calculation.
Benefits and Limitations
Benefits
Provides a quick, free reference figure for educational and general interest purposes.
Offers a choice of three widely recognised formulas for comparison.
Useful for students, carers and anyone researching how clinical dosing calculations work.
Limitations
Important: BSA formulas are estimates based on population averages and do not account for individual variations in body composition, such as high muscle mass or fluid retention. According to published clinical literature, formula choice can cause small but clinically relevant differences in precise dosing calculations, which is why real medical dosing must always be confirmed by a qualified professional.
Medical Disclaimer: This tool and article are for general information and educational purposes only and do not replace professional medical advice. Body surface area figures must always be confirmed by a doctor or pharmacist before being used for medication dosing. Read our full Disclaimer.
Frequently Asked Questions
A body surface area calculator estimates the total surface area of a person's body in square metres from their height and weight. It is widely used in clinical settings to guide medication dosing, particularly for chemotherapy, and to assess conditions such as burns.
The most common formula is the Mosteller formula: BSA (m²) equals the square root of (height in cm multiplied by weight in kg, divided by 3600). Other recognised formulas include DuBois and Haycock.
An average adult body surface area is roughly 1.7 to 2.0 square metres, though this varies with height, weight and body composition. There is no single fixed healthy number; BSA is used as a scaling reference rather than a pass or fail measure.
BSA correlates more closely than weight alone with metabolic rate, cardiac output and organ function, which is why many chemotherapy and paediatric drug doses are calculated per square metre of body surface area rather than per kilogram.
Both are widely used and produce similar results for most adults. The Mosteller formula is simpler to calculate and is now the most commonly used in clinical practice, while the DuBois formula was historically the standard reference.
Yes, BSA formulas such as Mosteller and Haycock are used for both adults and children, and BSA-based dosing is particularly common in paediatric medicine. Always confirm paediatric doses with a qualified clinician or pharmacist.
BMI estimates weight status relative to height, while BSA estimates the total surface area of the skin. BSA is mainly used clinically for dosing and physiological calculations, whereas BMI is used to screen for underweight, healthy weight, overweight and obesity. See our BMI Calculator NHS for weight-status screening.
No. BSA-based dosing should only be calculated and confirmed by a doctor, pharmacist or other qualified healthcare professional. This calculator is for general informational and educational purposes only.
Conclusion
This free body surface area calculator gives you an instant, formula-based estimate of your BSA in square metres, using the same Mosteller, DuBois and Haycock methods referenced in clinical literature. While BSA plays an important role in medication dosing and burns assessment, it should always be confirmed by a healthcare professional for any real clinical decision. For everyday health screening, our BMI Calculator NHS and related tools remain the more relevant starting point.
Last updated: January 2026 Created by: BMI Calculator NHS Editorial Team Reviewed by: NHS-Aligned Health Review Panel