Is BSA dosing the same as dosing by ideal body weight?

No. BSA dosing uses square meters (m²) from height and weight, while IBW dosing uses a height-based weight estimate. Medication protocols specify which method to use.

What is body surface area (BSA)?

BSA is the measured or calculated surface area of the human body, expressed in square meters (m²). It correlates with metabolic rate, cardiac output, and blood volume better than weight alone, making it useful for drug dosing and physiological calculations.

What is BSA used for in medicine?

BSA is used for chemotherapy dosing (mg/m²), calculating cardiac index (cardiac output ÷ BSA), determining GFR indexed to body size (mL/min/1.73m²), estimating burn extent (%TBSA), radiation therapy planning, and fluid resuscitation calculations.

What is a normal BSA for adults?

Average BSA is approximately 1.7 m² for women and 1.9 m² for men. Most adults fall between 1.5 and 2.2 m². Athletes and tall individuals may exceed 2.0 m², while smaller adults may be below 1.6 m².

Which BSA formula is most accurate?

No formula is definitively most accurate. Du Bois (1916) is the traditional standard. Mosteller (1987) produces nearly identical results with simpler math. Haycock (1978) is often preferred for pediatrics. Modern 3D scanning studies suggest all formulas are within ~5% of measured BSA for most patients.

What is the Du Bois formula?

The Du Bois formula (1916) is: BSA = 0.007184 × height^0.725 × weight^0.425, where height is in cm and weight is in kg. It was derived from direct measurements of 9 subjects and remains the most widely used formula despite its small derivation cohort.

What is the Mosteller formula?

The Mosteller formula (1987) is: BSA = √(height × weight / 3600), where height is in cm and weight is in kg. It's a mathematical simplification of Du Bois that's easier to calculate at the bedside or mentally, with nearly identical results.

Why is BSA used instead of weight for chemotherapy?

BSA correlates better with drug clearance and organ function than weight alone. Chemotherapy drugs have narrow therapeutic windows — too little is ineffective, too much is toxic. BSA-based dosing reduces variability in drug exposure between patients of different sizes.

How does obesity affect BSA calculations?

BSA increases with obesity, but drug metabolism doesn't scale proportionally because adipose tissue has lower blood flow. This can lead to overdosing. Many protocols cap BSA at 2.0 m² or use adjusted body weight for obese patients to prevent toxicity.

Is BSA different for children?

Yes. Children have proportionally larger heads and different body proportions than adults. The Haycock formula, validated in infants and children, is often preferred in pediatrics. BSA-based dosing is standard in pediatric oncology.

How do I calculate a drug dose from BSA?

Multiply the BSA by the dose in mg/m². Example: If the protocol calls for 75 mg/m² and the patient's BSA is 1.8 m², the dose is 75 × 1.8 = 135 mg. Always verify the calculation and round according to available formulations.

What is cardiac index and how does BSA relate?

Cardiac index (CI) = cardiac output ÷ BSA. Normal CI is 2.5–4.0 L/min/m². By dividing by BSA, cardiac output is normalized for body size, allowing comparison across patients. A cardiac output of 4 L/min is normal for a small person but low for a large person.

How is BSA used in burn assessment?

Burn severity is expressed as %TBSA (percent total body surface area burned). The Rule of Nines estimates body regions: each arm = 9%, each leg = 18%, anterior torso = 18%, posterior torso = 18%, head = 9%, perineum = 1%. %TBSA determines fluid resuscitation using formulas like Parkland (4 mL × kg × %TBSA).

Can BSA change over time?

Yes. BSA changes with weight gain or loss. Cancer patients often lose significant weight during treatment, decreasing BSA. Recalculating BSA at each treatment cycle ensures accurate dosing. A 10 kg weight loss in a 70 kg patient reduces BSA by approximately 0.1 m².

Why is GFR indexed to 1.73 m²?

The value 1.73 m² was the average BSA of young American adults in 1927 when this convention was established. Indexing GFR to a standard BSA allows comparison between patients of different sizes. An absolute GFR of 60 mL/min means different things in a 50 kg vs. 100 kg patient; indexing normalizes this.

Are there BSA calculators in electronic medical records?

Yes. Most EMRs and pharmacy systems calculate BSA automatically when height and weight are entered. However, clinicians should understand the underlying calculation, verify the formula used matches their protocol, and catch data entry errors that could affect dosing.

Online Medical Tools — BSA Calculator

Printed on 8/14/2026

For informational purposes only. This is not medical advice.

Body Metrics

BSA Calculator

Body surface area (BSA) is a critical measurement in medicine, used to calculate chemotherapy doses, derive cardiac index, and estimate burn severity. This calculator provides results from three validated formulas — Du Bois, Mosteller, and Haycock — allowing clinicians to choose the most appropriate method for their patient population. BSA depends on accurate height and weight — also calculate BMI Calculator and Ideal Weight Calculator. BSA is used to normalize cardiac index — assess cardiac risk with ASCVD Risk Calculator. In oncology patients, monitor renal function for chemotherapy dosing with eGFR Calculator or Creatinine Clearance (carboplatin dosing uses Calvert formula with CrCl).

Formula: Du Bois: BSA = 0.007184 × height^0.725 × weight^0.425

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Weight

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How It Works

Enter height and weight

Input your height in cm (or feet/inches) and weight in kg (or lbs). Use the unit toggle to switch between metric and imperial measurements.

View BSA from multiple formulas

The calculator computes your BSA using Du Bois (standard), Mosteller (simplified), and Haycock (pediatric-friendly) formulas. Results are shown in square meters (m²).

Apply to clinical calculations

Use your BSA to calculate drug doses (mg/m²), cardiac index, or burn percentage. Most oncology protocols use the Du Bois or Mosteller formula.

Who Uses the BSA Calculator

Chemotherapy Dosing

Oncologists & pharmacists

Nearly all cytotoxic chemotherapy protocols dose by BSA (mg/m²). Accurate BSA calculation is critical for efficacy and avoiding toxicity with narrow-therapeutic-index drugs.

Cardiac Index Calculation

Cardiologists & intensivists

Cardiac index (CI = cardiac output ÷ BSA) normalizes heart function for body size. CI helps assess hemodynamic status independent of patient size in ICU and cath lab settings.

Burn Assessment

Emergency & burn specialists

Burn severity is expressed as percent total body surface area (%TBSA). BSA calculation helps determine fluid resuscitation needs using formulas like Parkland.

Pediatric Dosing

Pediatricians & neonatologists

BSA-based dosing is standard in pediatric oncology and some other medications. The Haycock formula is often preferred for infants and children.

Renal Function Assessment

Nephrologists

GFR is often indexed to BSA (mL/min/1.73m²) to allow comparison across patients of different sizes. This standardization is essential for CKD staging.

Radiation Therapy Planning

Radiation oncologists

Some radiation dosimetry calculations incorporate BSA when determining treatment fields and doses for certain malignancies.

Pro Tips

Know which formula your protocol requires

Most oncology protocols use Du Bois or Mosteller, but some specify one formula. Using the wrong formula can change doses by 5–10%, which matters for narrow-therapeutic-index drugs.

Mosteller is easier for bedside calculation

Mosteller formula: BSA = √(height × weight / 3600). It's simpler than Du Bois and produces nearly identical results for most adults — ideal for quick mental math.

Use Haycock for pediatric patients

The Haycock formula was validated in children and is more accurate at lower heights and weights. Many pediatric oncology centers standardize on Haycock.

Consider BSA capping in obese patients

Many protocols cap BSA at 2.0 m² for obese patients because drug clearance doesn't scale linearly with body size. Check your specific protocol's guidelines.

Actual weight vs. ideal weight matters

For obese patients, some protocols use adjusted body weight (ABW = IBW + 0.4 × (actual − IBW)) instead of actual weight. This prevents overdosing lipophilic drugs.

Measure height, don't estimate

Self-reported height is often inaccurate (people overestimate). For chemotherapy dosing, measure height with a stadiometer. A 5 cm error changes BSA by ~0.05 m².

Recalculate BSA if weight changes significantly

Cancer patients often lose or gain weight during treatment. Recalculate BSA at each cycle to avoid under- or overdosing as body composition changes.

Small BSA differences can matter

A BSA change from 1.75 to 1.85 m² increases a 100 mg/m² dose from 175 mg to 185 mg — a 6% difference. For drugs like doxorubicin with cumulative toxicity, this adds up.

BSA is an estimate, not exact measurement

All BSA formulas are mathematical approximations. True body surface area requires 3D scanning. The formulas agree within ~5% for most patients, which is acceptable for clinical use.

Document which formula you used

When calculating drug doses, note the formula used in the medical record. This ensures consistency if another provider recalculates and enables accurate dose tracking.

Common Questions About Your Results

Evidence-Based Methodology

This calculator implements the Du Bois (1916), Mosteller (1987), and Haycock (1978) formulas. The Du Bois formula remains the clinical standard referenced in most chemotherapy protocols and drug dosing guidelines. Mosteller's simplified formula was published in the New England Journal of Medicine and is widely used for bedside calculations.

Clinical Content Trust

Last reviewed:: April 21, 2026
Guideline version:: General evidence framework v2026.04
Source set version:: Primary-source set v1

How to Interpret Your Result

Your BSA is reported in square meters (m²). The average adult BSA is approximately 1.7 m² for women and 1.9 m² for men, though values typically range from 1.5 to 2.2 m². The result itself does not indicate health or disease — it is a physiological parameter used as an input for other clinical calculations.

When BSA is used for drug dosing, the standard dose is typically expressed as mg/m². For example, a chemotherapy dose of 75 mg/m² for a patient with a BSA of 1.8 m² would yield a calculated dose of 135 mg. Small differences in BSA can meaningfully change the final dose, particularly for drugs with narrow therapeutic windows.

When to Use This Tool

BSA is most commonly needed when calculating chemotherapy doses, as nearly all cytotoxic drug protocols are BSA-based. It is also used to derive the cardiac index (cardiac output divided by BSA), which helps assess heart function independent of body size.

Other clinical uses include calculating renal function parameters, estimating fluid requirements, and assessing the extent of burn injuries (where BSA of the burn is expressed as a percentage of total body surface area).

Limitations

BSA formulas were derived from relatively small, historically non-diverse study populations. The original Du Bois formula (1916) was based on only 9 subjects. While later formulas like Mosteller and Haycock used larger datasets, all are mathematical approximations of a complex three-dimensional measurement.

In obese patients, BSA-based dosing can lead to supratherapeutic drug levels because BSA increases with weight, but drug clearance does not scale proportionally. Many oncology protocols cap BSA at 2.0 m² or use adjusted body weight for very obese patients. Similarly, in cachectic or very small patients, BSA-based doses may need clinical adjustment.

Different formulas can produce slightly different results (typically within 5–10%), which may matter for narrow-therapeutic-index drugs.

Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.

Changelog

April 21, 2026 · trust-baseline
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