Body Surface Area Calculator (BSA)

Use the Body Surface Area (BSA) Calculator

Enter height and weight, choose a formula (Mosteller by default), and review BSA in m². The BSA calculator is intended for education and protocol review—always follow local dosing policies.

How to Use Body Surface Area Calculator (BSA)

1. Step 1: Select Units

   Choose Metric (cm, kg) or US/Imperial (ft/in, lb) so your height and weight are interpreted correctly.

2. Step 2: Enter Height

   Type your height in centimeters or in feet and inches. Stay within realistic ranges to avoid errors.

3. Step 3: Enter Weight

   Type your body weight in kilograms or pounds. Decimals are OK.

4. Step 4: Pick Preferred Formula

   Mosteller is commonly used for dosing. You can also compare Du Bois, Haycock, Boyd, and Gehan–George.

5. Step 5: Calculate and Review

   Tap Calculate to see BSA in m² for all formulas, then review the notes before applying results in care plans.

Key Features

• Multiple formulas
• Medical dosing
• Metric/Imperial
• Clinical use

Understanding Results

Formula

Body surface area (BSA) is estimated from height and weight. A practical standard is the Mosteller equation: BSA = √((height (cm) × weight (kg)) / 3600). Other frequently used equations include Du Bois (0.007184 × W^0.425 × H^0.725), Haycock (0.024265 × W^0.5378 × H^0.3964), Gehan–George (0.0235 × W^0.51456 × H^0.42246), and Boyd, which adjusts the weight exponent using a logarithmic term.

All formulas report BSA in square meters (m²). Differences between methods are usually small (within a few percent), but your institution may standardize on one formula for consistency. In chemotherapy and pediatrics, Mosteller is commonly preferred for its simplicity and reliable performance across body sizes.

Reference Ranges & Interpretation

Typical adult BSA is roughly 1.6–1.9 m², but values vary with height, weight, sex, and population norms. Larger individuals have higher BSA; smaller adults and children have lower BSA. BSA is often used to scale medication doses with narrow therapeutic windows, helping to approximate exposure while accounting for body size.

Because BSA is derived from height and weight, it describes size rather than composition. Two people with the same BSA may have different body fat and lean mass. For drugs influenced by fat‑free mass or renal function, clinicians may use additional measures alongside BSA.

Body Surface Area Calculator: tips for dosing

Confirm units, measure height/weight accurately, and document the chosen formula. Recalculate if values are estimated or conditions change, and always defer to institutional protocols for prescribing.

Assumptions & Limitations

BSA is an estimate. It does not account for edema, ascites, amputations, or extreme body composition, and it is not a substitute for organ function or therapeutic drug monitoring. Some therapies use fixed dosing or area‑under‑the‑curve models instead of BSA. Always follow local protocols, double‑check math, and apply clinical judgment before prescribing.

Complete Guide: Body Surface Area Calculator (BSA)

Calculate BSA with our body surface area calculator for clinical use. Essential and precise computation for medication dosing and chemotherapy protocols.

This body surface area calculator implements several established equations side‑by‑side so you can compare results, pick a preferred method for your organization, and keep your workflow consistent and fast.

What is Body Surface Area (BSA)?

Body surface area is an estimate of the area covering the outside of the human body. It is expressed in square meters (m²) and is derived from height and weight. BSA is commonly used to scale medication doses—especially in oncology and pediatrics—because it loosely correlates with factors that influence drug distribution and heat exchange. BSA is not a direct measurement; you cannot easily measure total skin area in practice, so clinicians rely on validated equations to estimate it.

In adults, typical BSA spans about 1.6–1.9 m², though healthy ranges extend beyond this depending on height, weight, and population. Children naturally have smaller values, which increase as they grow. Because BSA links dose to body size, many protocols standardize their preferred formula to keep dosing consistent across teams.

Historically, BSA equations were developed from body measurements and limited direct surface mapping. Early work by Du Bois and Du Bois established an allometric model relating BSA to weight and height, while later formulas—like Mosteller and Haycock—emphasized simplicity and broad applicability. Despite the methodological differences, modern formulas usually agree closely for most patients when used within typical adult and pediatric ranges.

How this calculator works

Enter height and weight using Metric (cm, kg) or US/Imperial (ft/in, lb). The tool converts units internally and computes BSA using multiple common equations in parallel: Mosteller, Du Bois, Haycock, Boyd, and Gehan–George. You can mark one as your preferred method—Mosteller is popular because it is simple and performs well across sizes—and the summary card highlights that value.

All outputs are shown to three decimals (m²), which aligns with typical rounding for medication dosing. Results between formulas usually differ only slightly; when institutional policy specifies a single equation, follow that policy for consistency in prescribing and documentation.

Each formula has pedigree and nuance. Du Bois derives from early surface mapping studies; Haycock was built with pediatric performance in mind; Boyd refines the weight exponent using a log term to better accommodate a wide weight range; and Gehan–George is another well‑cited model. In everyday practice, the differences tend to be small, but choosing one method for all orders minimizes ambiguity when verifying doses across clinics and pharmacies.

Units and conversion

BSA equations use height and weight. Standard inputs are centimeters for height and kilograms for weight. If you work in feet‑inches and pounds, choose US/Imperial and the calculator will handle conversions internally and still report BSA in m². Unit switches are fully reversible: you can convert displayed values back and forth without losing precision.

For daily use, keep entries realistic (for example, heights 90–260 cm and weights 20–350 kg). Extremely small or large numbers can make equations unstable or fall outside clinical validation. When values are outside typical human ranges, confirm the source data or re‑measure.

Example calculations

Consider someone who is 170 cm tall and weighs 70 kg. Using the Mosteller equation: BSA = √((170 × 70) / 3600) ≈ √(3.3056) ≈ 1.818 m². Du Bois, Haycock, Boyd, and Gehan–George produce values within a few hundredths of a square meter of that result. Small differences are normal and usually not clinically meaningful when protocols specify a single method.

If you enter 5 ft 7 in and 154 lb (the same person in Imperial units), the calculator converts to the same metric inputs and returns the same BSA values. This ensures consistency across unit systems and supports teams that switch between documentation standards.

Pediatric considerations

BSA is widely used in pediatrics, where body size changes rapidly with age. Mosteller and Haycock are frequently used for children because they perform well across the pediatric size spectrum. In neonates and infants, even small measurement errors can shift BSA, so re‑measure if anything looks off. Always consult pediatric protocols for dose caps, maximum single doses, and infusion rates that may supersede BSA alone.

For pediatric dosing workflows, you may also reference weight‑based calculators and growth‑related tools on our site. If you are checking development or nutrition questions, related resources include the Child BMI Percentile Calculator and the Toddler Growth Percentile Calculator.

BSA in oncology dosing

BSA‑based dosing has a long history in chemotherapy. Many regimens scale doses to m² to help normalize exposure across body sizes. However, modern practice may also use fixed dosing, dose capping, or pharmacokinetic targets (for example, AUC‑based carboplatin) depending on the agent and protocol. Institutions often standardize on a single BSA formula—commonly Mosteller—to reduce variation in orders, dispensing, and auditing.

If you work with infusions or compounding, you may also find our mg/mL Dose Calculator and Pediatric Dose Calculator helpful alongside BSA. For a general overview from a trusted source, see the National Cancer Institute’s chemotherapy overview (NCI).

Some protocols cap BSA at thresholds such as 2.0 m² to avoid excessive doses in very large bodies, while others rely on toxicity‑guided adjustments cycle by cycle. Always check the latest regimen sheet: dose calculation rules can differ across drugs, lines of therapy, and clinical trials. When BSA changes meaningfully during a treatment course—because weight changes—teams often re‑calculate before each cycle.

BSA vs BMI vs Lean Body Mass

BSA, body mass index (BMI), and lean body mass (LBM) capture different aspects of body size. BSA is most often a dosing scaler. BMI (kg/m²) classifies weight relative to height and is useful for population risk, not dosing. LBM estimates fat‑free mass and may correlate with drug distribution for certain agents. No single index is best in every situation, so clinicians often consider several metrics together.

If you want to explore adjacent measures, try our Adult BMI Calculator, Lean Body Mass Calculator, and Body Fat Percentage Calculator. These tools complement BSA by describing different dimensions of body composition and size.

In practice, BMI can help identify underweight, normal weight, overweight, and obesity categories that inform nutrition and risk counseling, while LBM can guide discussions about sarcopenia or cachexia. BSA sits alongside these as an engineering‑style scaler for dosing. When indices disagree or give conflicting messages, anchor decisions in clinical status, lab values, and the specific pharmacology of the medication being considered.

Renal function and AUC‑based dosing

For drugs cleared by the kidneys, dosing may depend more on renal function than on BSA. Carboplatin is a classic example: clinicians target exposure (AUC) using formulas that incorporate creatinine clearance. In such cases, BSA can be secondary to kidney function or not used at all. Always follow agent‑specific guidance.

You can estimate renal function with our Creatinine Clearance Calculator, then combine that knowledge with BSA if your protocol requires both. For broader energy needs, the BMR Calculator and Calorie Calculator may also be useful in nutrition‑oriented care plans.

Practical tips for accurate entry and privacy

Measure carefully. Round only at the end if your protocol requires rounding to the nearest 0.01 or 0.1 m². Confirm unusual values with a re‑measurement. If height or weight is estimated (for example, when a patient cannot stand), note the estimation method in your documentation and consider the potential impact on dosing.

This tool is privacy‑first: it runs completely in your browser and does not store or send personal data. You can use it confidently at the bedside or in clinic without creating an identifiable record in the app. If you need to keep a value for your chart, copy it to your note or record it in the EHR according to policy.

Limitations and when to use alternatives

BSA is not perfect. It does not capture body composition, fluid status, or organ dysfunction. Ascites, edema, and amputations change body size in ways the equations do not model. For some therapies, fixed dosing, therapeutic drug monitoring, or pharmacokinetic approaches are preferred. Renal or hepatic adjustments, dose caps, or maximum single‑dose limits may overrule BSA entirely.

Use clinical judgment. Review the full protocol for each drug and confirm which BSA equation—if any—is required. When weight changes significantly during a treatment course, many teams re‑measure height when reasonable and update weight at each cycle to keep calculations current.

When BSA seems inconsistent with your broader assessment—for example, in cases of severe edema or dehydration—consider whether an alternative framework (fixed dose, AUC target, or organ‑function‑based adjustment) is recommended for that agent. Carefully document the rationale behind dose selection, especially when deviating from standard weight‑ and BSA‑based approaches.

Related tools on this site

Explore more calculators that often appear in the same workflows: the Ideal Body Weight Calculator, Waist‑to‑Height Ratio Calculator, Calorie Calculator, and BMR Calculator. Each tool answers a slightly different question and can complement BSA during assessment and planning.

Frequently Asked Questions