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Body Surface Area Calculator
Calculate body surface area using DuBois, Mosteller, Haycock, and Boyd formulas with comparison to average.
Body Surface Area Calculator
Free online Body Surface Area (BSA) calculator with Du Bois, Mosteller, Haycock, and Boyd formulas. Used in medical drug dosing and burn assessment.
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Body Surface Area (BSA) is the total external skin surface of the human body, measured in square meters (m²). The Mosteller formula — BSA = √(Height(cm) × Weight(kg) / 3600) — is the most widely used in clinical practice due to its simplicity. The Du Bois formula (0.007184 × W0.425 × H0.725) is the historical standard in cardiology and pharmacology. Average adult BSA: males ~1.9 m², females ~1.6 m². BSA drives chemotherapy dosing (mg/m²), cardiac output indexing (cardiac index = CO / BSA), and burn area assessment via the Rule of Nines.
📐 Body Surface Area — Complete Guide
Reviewed by CalculatorApp.me Health Editorial Team · Updated June 2026 · 10 min read
Why BSA Matters in Medicine
Body Surface Area (BSA) is the total external skin surface measured in square meters (m²). Unlike body weight, BSA better reflects metabolic mass because organ size, cardiac output, and renal function correlate more closely with surface area than mass alone.
The most common clinical application is chemotherapy dosing — drugs with narrow therapeutic windows (too much causes toxicity, too little is ineffective) are dosed in mg/m² BSA to normalize across body sizes. BSA-based dosing was introduced in the 1950s and remains the standard for most cytotoxic agents.
Other uses include calculating cardiac index (cardiac output / BSA), glomerular filtration rate normalization, and burn area estimation using the Rule of Nines (each body region = 9% BSA).
Clinical Applications of BSA
- ▸Chemotherapy dose calculation (mg/m²)
- ▸Cardiac index (CI = CO / BSA)
- ▸GFR normalization (mL/min/1.73 m²)
- ▸Burn area assessment (Rule of Nines)
- ▸Pediatric drug dosing
- ▸IV fluid requirements in burns
- ▸Normal range definition for cardiac output
- ▸Dermatology: body surface area involvement
BSA Formula Comparison
| Formula | Year | Equation | Best Use |
|---|---|---|---|
| Mosteller | 1987 | √(H(cm) × W(kg) / 3600) | Clinical practice (simplest, most used) |
| DuBois & DuBois | 1916 | 0.007184 × W⁰·⁴²⁵ × H⁰·⁷²⁵ | Cardiology, pharmacology (historical gold standard) |
| Gehan & George | 1970 | 0.0235 × H⁰·⁴²²⁴⁶ × W⁰·⁵¹⁴⁵⁶ | Research, larger sample validation |
| Haycock | 1978 | 0.024265 × H⁰·³⁹⁶⁴ × W⁰·⁵³⁷⁸ | Pediatric populations |
| Dubois (simplified) | 2010 | 0.20247 × H(m)⁰·⁷²⁵ × W(kg)⁰·⁴²⁵ | Emergency/bedside estimate |
All formulas produce similar results for average adults (within 5%). Differences become meaningful in very obese, very thin, or pediatric patients.
BSA Myths vs Facts
Frequently Asked Questions
Why do doctors use BSA instead of body weight for chemotherapy?›
BSA better accounts for the relationship between body size and metabolic processes like drug clearance. The hypothesis (from 1958 studies) is that metabolic rate scales with BSA rather than mass — though this is debated for all drug classes. BSA dosing reduces variability in drug exposure between patients of different sizes.
What is the Mosteller formula and why is it preferred?›
Mosteller (1987): BSA = √(height(cm) × weight(kg) / 3600). It's preferred in clinical practice because it's simple enough to calculate mentally or with a basic calculator, yet produces results within 2–3% of more complex formulas for average adults.
What is a normal BSA for an adult?›
Average adult male: ~1.9 m² (range 1.7–2.1 m²). Average adult female: ~1.6 m² (range 1.5–1.8 m²). BSA increases with height and weight. The "standard" 1.73 m² used to normalize GFR was derived from historical average values and may underrepresent modern body sizes.
How does the Rule of Nines use BSA?›
In burn medicine, BSA is divided into regions: head and neck = 9%, each arm = 9%, each leg = 18% (thigh + lower leg), front torso = 18%, back torso = 18%, perineum = 1%. This allows rapid estimation of burn extent (% TBSA — total body surface area) to guide fluid resuscitation.
Is BSA useful for everyday health tracking?›
BSA is primarily a clinical metric, not a personal health monitoring tool. For daily health tracking, BMI, body fat percentage, waist circumference, and waist-to-height ratio are more practical. BSA is most useful if you or a family member is receiving dose-calculated medications.
How accurate is BSA calculation from height and weight?›
For average adults (BMI 18.5–30), BSA formulas are accurate within ±5% compared to direct measurement. For very obese patients (BMI >35), most formulas underestimate true BSA. 3D body scanning is the most accurate method but impractical clinically.
What is cardiac index and how is BSA used?›
Cardiac index (CI) = cardiac output (CO) / BSA. Normal CI is 2.5–4.0 L/min/m². Normalizing CO for BSA allows comparison between patients of different body sizes. A CO of 5 L/min is normal for someone with 2.5 m² BSA, but may indicate reduced cardiac function for someone with 2.0 m² BSA.
How is BSA calculated for children?›
The Haycock formula is most validated for pediatrics: 0.024265 × H(cm)⁰·³⁹⁶⁴ × W(kg)⁰·⁵³⁷⁸. Pediatric chemotherapy protocols strictly use BSA-based dosing. For very young infants (<10 kg), weight-based dosing with BSA verification is used due to limited formula validation data.
References & Further Reading
- • Mosteller RD — Simplified Calculation of Body-Surface Area, NEJM 1987;317:1098
- • DuBois D, DuBois EF — A formula to estimate the approximate surface area if height and weight be known, Arch Intern Med 1916;17:863-871
- • Haycock GB et al. — Geometric method for measuring body surface area, J Pediatr 1978;93:62-66
- • Pinkel D — The use of body surface area as a criterion of drug dosage in cancer chemotherapy, Cancer Res 1958;18:853
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Body Surface Area (BSA) Calculator — Complete Guide
Du Bois, Mosteller, and Haycock formulas, drug dosing, burn assessment, and clinical applications.
1.7 m²
Average adult BSA
Du Bois
Gold-standard formula
mg/m²
Drug dosing unit
9s Rule
Burn area assessment
What Is Body Surface Area?
Body Surface Area (BSA) is the measured or calculated total area of the external surface of the human body, expressed in square meters (m²). The average adult BSA is approximately 1.7 m² (1.9 m² for males, 1.6 m² for females). BSA is a critical clinical parameter because many physiological processes — metabolic rate, drug clearance, cardiac output, fluid requirements — correlate more closely with surface area than with body weight alone.
BSA cannot be directly measured in clinical practice (unlike weight), so it is always estimated using formulas that take height and weight as inputs. The relationship between BSA and body size follows a power-law curve: BSA scales proportionally to height0.725 × weight0.425 (the Du Bois exponents), meaning taller and heavier individuals have disproportionately more surface area.
The most critical clinical application of BSA is chemotherapy dosing. Since the 1950s, cytotoxic drug doses have been prescribed in mg/m² rather than mg/kg to account for the wide variation in drug clearance between patients of different sizes. BSA-based dosing reduces toxicity without sacrificing efficacy.
BSA Calculation Formulas
BSA = 0.007184 × H^0.725 × W^0.425
Where:
BSA = body surface area (m²)
H = height in centimeters
W = weight in kilograms
Example: 175 cm, 80 kg
BSA = 0.007184 × 175^0.725
× 80^0.425
BSA = 0.007184 × 47.96
× 7.268
BSA = 0.007184 × 348.6
BSA = 1.95 m²
Derived from:
Direct measurement of 9 subjects
Coating method (paper/foil)
Validated over 100+ years
Most widely cited formula
Limitations:
• Only 9 subjects (all adults)
• Less accurate for extremes
(very obese, very small children)
• May underestimate by 3-8%
in obese patientsDespite being over 100 years old and based on only 9 subjects, the Du Bois formula remains the most commonly used BSA formula in clinical practice and drug dosing.
BSA = √(H × W / 3600) Where: H = height in cm W = weight in kg 3600 = constant (60²) Alternative (imperial units): BSA = √(H_in × W_lb / 3131) Example: 175 cm, 80 kg BSA = √(175 × 80 / 3600) BSA = √(14000 / 3600) BSA = √3.889 BSA = 1.97 m² Advantages: ✓ Simple enough for mental calc ✓ Only needs square root ✓ Results within 1-2% of Du Bois ✓ Easy to program/implement Widely used in: • Oncology departments • ICU protocols • Research publications
Mosteller published this as a 'simplified calculation of body-surface area' in the NEJM. Its simplicity made it the preferred formula for rapid clinical calculations.
BSA = 0.024265 × H^0.3964 × W^0.5378
Designed for all ages including:
Neonates (premature to term)
Infants and children
Adolescents
Adults
Example: Child — 120 cm, 25 kg
BSA = 0.024265 × 120^0.3964
× 25^0.5378
BSA = 0.024265 × 8.445
× 5.432
BSA = 0.024265 × 45.88
BSA = 0.91 m²
Example: Neonate — 50 cm, 3.5 kg
BSA = 0.024265 × 50^0.3964
× 3.5^0.5378
BSA = 0.024265 × 5.80
× 1.944
BSA = 0.024265 × 11.28
BSA = 0.27 m²
Preferred for:
Pediatric oncology
Neonatal drug dosing
Fluid resuscitationHaycock validated on 81 subjects from birth to adulthood. More accurate than Du Bois for children <30 kg and neonates — essential for pediatric doses where small errors have big consequences.
Gehan & George:
BSA = 0.0235 × H^0.42246
× W^0.51456
Boyd:
BSA = 0.0003207 × H^0.3
× W^(0.7285 − 0.0188×log₁₀(W))
Comparison at 175 cm, 80 kg:
Du Bois: 1.95 m²
Mosteller: 1.97 m²
Haycock: 1.96 m²
Gehan: 1.94 m²
Boyd: 1.96 m²
Differences are typically <3%
for normal-weight adults.
Greater divergence in:
• Morbid obesity (>40 BMI)
• Extreme heights (>200 cm)
• Neonates (<3 kg)
• Cachexia (cancer wasting)
Clinically: most protocols default
to Du Bois or Mosteller unless
the patient is pediatric (→ Haycock)Most BSA formulas agree within 2-3% for normal-sized adults. The choice matters most at the extremes — pediatric, morbidly obese, and cachectic patients.
Clinical Applications of BSA
| Application | How BSA Is Used | Why Not Body Weight | Example |
|---|---|---|---|
| Chemotherapy Dosing | Dose in mg/m² (e.g., 5-FU 400 mg/m²) | Drug clearance correlates with BSA better than weight | BSA 1.8 m² × 400 mg/m² = 720 mg |
| Burn Assessment | Rule of 9s maps body regions to %BSA | Total burn area (%TBSA) guides fluid resuscitation | Parkland: 4 mL × kg × %TBSA (1st 24h) |
| Cardiac Index | CI = Cardiac Output / BSA | Normalizes CO for body size comparison | CI = 5.0 L/min ÷ 1.7 m² = 2.9 L/min/m² |
| GFR Normalization | eGFR standardized to 1.73 m² | Enables comparison across body sizes | GFR × (1.73/patient BSA) |
| Fluid Resuscitation | Maintenance rate linked to BSA | More accurate than weight-based for children | 1500 mL/m²/day maintenance |
| Organ Size Indices | LVMI = LV mass/BSA | Detects hypertrophy independent of body size | LVMI >95 g/m² (F) or >115 g/m² (M) |
BSA Normal Ranges by Age & Sex
| Age Group | Typical BSA (m²) | Height Range | Weight Range | Notes |
|---|---|---|---|---|
| Neonate (term) | 0.20-0.25 | 48-53 cm | 2.5-4.5 kg | Haycock formula preferred |
| Infant (1 yr) | 0.40-0.50 | 72-80 cm | 8-12 kg | Rapid BSA increase in 1st year |
| Child (5 yr) | 0.70-0.80 | 105-115 cm | 17-22 kg | Pediatric dosing critical |
| Adolescent (12 yr) | 1.20-1.40 | 148-160 cm | 38-50 kg | Approaching adult ranges |
| Adult Female | 1.45-1.75 | 155-170 cm | 50-75 kg | Mean ~1.60 m² |
| Adult Male | 1.70-2.10 | 170-185 cm | 65-95 kg | Mean ~1.90 m² |
| Large Adult | 2.10-2.50 | 185+ cm | 100+ kg | Chemo dose capping may apply |
| Elderly (>70) | 1.40-1.80 | Decreasing | Variable | Sarcopenia reduces BSA |
History of Body Surface Area Measurement
Meeh — First BSA Formula
German physiologist Karl Meeh proposed the first formula relating body surface area to body weight: BSA = k × W^(2/3). The constant k varied by species. This was the first mathematical attempt to estimate BSA but was limited by its single-variable approach — ignoring height.
Du Bois & Du Bois — The Definitive Formula
Delafield Du Bois and his cousin Eugene F. Du Bois measured the surface area of 9 subjects using paper molds. They derived BSA = 0.007184 × H^0.725 × W^0.425 — incorporating both height and weight. Despite the tiny sample, this formula has remained the clinical standard for over a century.
Boyd Formula Published
Edith Boyd published an alternative formula using a larger validation cohort. Her formula used a logarithmic weight exponent, making it more complex but slightly more accurate for children. It saw limited clinical adoption due to computational difficulty before calculators.
BSA-Based Chemotherapy Dosing Begins
Oncologists began using mg/m² dosing for cytotoxic drugs after Pinkel showed that drug clearance correlated better with BSA than body weight. This became the standard for cancer treatment and remains the basis for nearly all chemotherapy protocols worldwide.
Haycock — Pediatric BSA Formula
Haycock, Schwartz, and Wisotsky validated a BSA formula across 81 subjects from neonates to adults. Their formula proved significantly more accurate for children under 10 kg — critical for pediatric oncology and neonatal intensive care where dosing errors can be fatal.
Mosteller Simplifies Calculation
R.D. Mosteller published a radically simplified formula: BSA = √(H×W/3600). Published as a letter in the NEJM, it could be calculated with a basic calculator — democratizing BSA estimation. It agrees with Du Bois within 1-2% for most adults and became the preferred formula in many clinical settings.
Key Research & Data
JCO — Mathijssen et al. (2007)
Should We Abandon BSA-Based Dosing?
Systematic review of BSA-based chemotherapy dosing: BSA explains only 15-35% of inter-patient variability in drug clearance. Despite this limitation, no alternative (flat dosing, pharmacogenomics, therapeutic drug monitoring) has consistently proven superior across drug classes. BSA-based dosing remains the pragmatic standard.
NEJM — Mosteller (1987)
Simplified Body-Surface Area Calculation
Introduced BSA = √(H×W/3600) — a formula accurate to within 1-2% of Du Bois for normal-sized adults. The simplicity enabled widespread adoption. Note: the original NEJM publication was a 1-paragraph letter that became one of the most cited medical formulas.
Burns — Lund-Browder Chart Validation
Accurate Burn Area Assessment
The Lund-Browder chart provides age-adjusted body region percentages for burn assessment, more accurate than the Rule of 9s for children (where head = 18% at birth vs 9% in adults). TBSA assessment accuracy directly affects fluid resuscitation volumes — critical for burn survival.
Du Bois & Du Bois — Archives (1916)
The Original BSA Formula
Measured 9 individuals by coating them with paper strips, cutting and weighing the paper. Derived the formula BSA = 0.007184 × H^0.725 × W^0.425. Despite the small sample size (criticized ever since), the formula has been validated in thousands of subjects and remains the reference standard.
BSA Myths vs. Facts
BSA-based dosing is perfectly accurate for all patients.
BSA explains only 15-35% of inter-patient drug clearance variability. Genetic factors, liver function, kidney function, and drug interactions play major roles. However, BSA is still the best simple metric available — therapeutic drug monitoring can fine-tune individual doses.
Weight-based dosing (mg/kg) is simpler and equally accurate.
Weight-based dosing systematically under-doses obese patients and over-doses small patients. BSA accounts for both height and weight, better reflecting metabolic size. For narrow therapeutic index drugs (chemotherapy), this difference can mean toxicity vs. under-dosing.
The Rule of 9s works for all ages.
The Rule of 9s (head=9%, each arm=9%, each leg=18%, trunk=36%, perineum=1%) is accurate for adults only. In infants, the head is ~18% and legs are ~14% each. The Lund-Browder chart provides age-adjusted percentages and is required for accurate pediatric burn assessment.
All BSA formulas give the same result.
For normal-weight adults, formulas agree within 2-3%. But for morbidly obese patients, Du Bois may underestimate by 10-15% vs. Mosteller. For premature neonates, Haycock is significantly more accurate. Formula choice matters at the clinical extremes.
Frequently Asked Questions
Why is BSA used instead of body weight for dosing?▼
What is the average BSA for adults?▼
How is BSA used in burn treatment?▼
Which formula is best for children?▼
What is the cardiac index?▼
How does obesity affect BSA calculations?▼
What is the Rule of 9s?▼
Can BSA be measured directly?▼
Why is eGFR normalized to 1.73 m²?▼
How does BSA change with age?▼
What is BSA-capped dosing?▼
How does BSA relate to BMI?▼
References
- Du Bois & Du Bois — A Formula to Estimate Approximate Surface Area (1916)
- Mosteller — Simplified BSA Calculation (NEJM, 1987)
- Haycock et al. — Body Surface Area in Infants and Children (J Pediatr, 1978)
- Mathijssen et al. — Should BSA Dosing Be Abandoned? (JCO, 2007)
- ASCO Guidelines — Chemotherapy Dosing for Obese Adults
- American Burn Association — Burn Assessment Guidelines
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