Body Surface Area Calculator

CalculatorApp.me

Part of:Blood Health & Vitals Guide 2026: Blood Pressure, Blood Type, BAC & Key Body Metrics

Professional review pending. Body Surface Area Calculator has passed formula and automated QA checks, but no independently verified clinician is currently attributed. Content updated June 21, 2026. Review process

Back to Health

Body Surface Area Calculator

No Intrusive AdsAI-Powered

Free online Body Surface Area (BSA) calculator with Du Bois, Mosteller, Haycock, and Boyd formulas. Used in medical drug dosing and burn assessment.

Height

Unit

Weight

Unit

Formula

Enter values above to see results.

About This Calculator

Want to learn more? Browse our calculation guides and tutorials →

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 × W^0.425 × H^0.725) 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

🏥 Clinical Standard

1.9 m²

Average BSA for adult males

1.6 m²

Average BSA for adult females

mg/m²

How chemotherapy doses are prescribed

DuBois

Gold standard formula since 1916

Formulas ComparedClinical UsesChemo DosingBurn AssessmentMyths vs FactsFAQs

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

✗MYTH: BSA and body weight measure the same thing

✓FACT: BSA and weight correlate but are not equivalent. A person who gains 20 kg of fat increases weight by 20% but BSA by only ~6%. Chemotherapy dosed by weight would overdose obese patients; BSA dosing is more accurate.

✗MYTH: All BSA formulas give identical results

✓FACT: While results are similar for average adults, formulas diverge for extreme body sizes. The DuBois formula underestimates BSA in obese patients; the Haycock formula was specifically validated for children.

✗MYTH: BSA is only relevant for cancer treatment

✓FACT: BSA is used in cardiology (cardiac index normal: 2.5–4.0 L/min/m²), nephrology (GFR is normalized to 1.73 m²), burn treatment, and dermatology (psoriasis PASI scoring uses % BSA involved).

✗MYTH: A higher BSA means you're overweight

✓FACT: BSA increases with both height and weight. A tall, athletic person may have a higher BSA than a shorter, heavier person. BSA is not a measure of adiposity or health status.

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

Related Calculators

Explore All Health Calculators

Body composition, clinical metrics, nutrition, and wellness tools — all free.

Health Calculators →All Calculators →

Body Surface Area Calculator

Calculate body surface area using DuBois, Mosteller, Haycock, and Boyd formulas with comparison to average.

Reviewed by CalculatorApp.me Health Team

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 height^0.725 × weight^0.425 (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

Du Bois & Du Bois (1916) — Standard

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 patients

Despite 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.

Mosteller Formula (1987) — Simplified

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.

Haycock Formula (1978) — Pediatric

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 resuscitation

Haycock 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 (1970) & Boyd (1935)

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

1879

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.

1916

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.

1935

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.

1958

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.

1978

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.

1987

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?▼

Many drugs distribute into tissues proportional to BSA rather than weight. BSA correlates better with organ size, blood volume, basal metabolic rate, and glomerular filtration rate — all factors in drug distribution and clearance. This is especially true for drugs with narrow therapeutic indices.

What is the average BSA for adults?▼

Average adult BSA is ~1.73 m² (the value used to normalize GFR). Males average ~1.9 m² and females ~1.6 m². The 1.73 m² standard was established in the early 1900s — modern populations may average slightly higher due to increases in body size.

How is BSA used in burn treatment?▼

The percentage of total BSA (%TBSA) affected by burns determines fluid resuscitation. The Parkland formula (4 mL × kg × %TBSA over 24 hours) calculates IV fluid requirements. Only second-degree and deeper burns are counted — superficial burns (1st degree) are excluded.

Which formula is best for children?▼

The Haycock formula is recommended for pediatric patients, especially neonates and infants under 10 kg. Du Bois and Mosteller were derived from adult populations and may underestimate BSA in small children, leading to underdosing of critical medications.

What is the cardiac index?▼

Cardiac index (CI) = Cardiac output ÷ BSA. Normal CI is 2.5-4.0 L/min/m². It normalizes cardiac output for body size, allowing comparison between patients. CI < 2.2 indicates cardiogenic shock; CI > 4.0 may indicate sepsis or hyperthyroidism.

How does obesity affect BSA calculations?▼

Obese patients have higher BSA, but the increase is proportionally less than the weight increase (because BSA scales with weight^0.425, not linearly). This means mg/m² dosing in obese patients may result in higher total doses but lower doses per kg — sometimes requiring dose capping at BSA = 2.0 m².

What is the Rule of 9s?▼

A quick clinical tool: head = 9%, each arm = 9%, anterior trunk = 18%, posterior trunk = 18%, each leg = 18%, perineum = 1%. The patient's palm (including fingers) ≈ 1% BSA. Used for rapid field assessment of burn area but less accurate for children and obese patients.

Can BSA be measured directly?▼

Historically, BSA was measured by coating the body surface with paper or aluminum foil, removing it, and calculating the area. Modern 3D body scanners can measure BSA directly, but the cost and complexity make formula-based estimation standard practice.

Why is eGFR normalized to 1.73 m²?▼

The 1.73 m² value was the average BSA of 25-year-old Americans when GFR standards were established in the 1920s. Normalizing GFR to this standard (mL/min/1.73 m²) allows comparison across body sizes. For drug dosing in extremes of body size, 'de-normalized' (absolute) GFR should be used.

How does BSA change with age?▼

BSA increases rapidly in childhood (0.25 m² at birth to ~1.0 m² by age 8), plateaus in early adulthood, and may decrease slightly in the elderly due to height loss and sarcopenia. Lifelong tracking isn't needed — BSA is calculated at each clinical encounter.

What is BSA-capped dosing?▼

Some oncology protocols cap BSA at 2.0 m² for dose calculation, meaning patients with BSA > 2.0 m² receive the same dose as a 2.0 m² patient. This is controversial — ASCO guidelines recommend using actual BSA for most chemotherapy, as capping may lead to underdosing in larger patients.

How does BSA relate to BMI?▼

BMI (kg/m²) and BSA (m²) both use height and weight but measure different things. BMI estimates adiposity; BSA estimates surface area. A high BMI doesn't always mean high BSA — a short, obese person may have lower BSA than a tall, normal-weight person.

References

Related Calculators

🔥

TDEE Calculator

Metabolic rate & energy

❤️

Blood Pressure

Cardiac index needs BSA

🥩

Protein Calculator

Nutrition by body size

🏋️

One Rep Max

Strength per body weight

🤰

Due Date Calculator

Pediatric BSA planning

😴

Sleep Calculator

Recovery optimization

Explore All Health Calculators

Precision health metrics for clinical and personal use — CalculatorApp.me.

Browse Health Calculators →

Methodology, sources & limitations

This calculator uses a published formula and the values entered in the calculator to generate the result.

Formula: BSA = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425
Jurisdiction & units: Intended for US, IN, EU, GB, Global. Supports both units where applicable.
Assumptions & limitations: Results are screening or educational estimates based on the inputs you provide. They do not diagnose, treat, or replace advice from a qualified clinician.
Review status: Formula and automated QA completed June 21, 2026; independent professional review is pending. Next scheduled review: September 21, 2026.

Validation sources

Du Bois & Du Bois (1916)
Mosteller (1987)
Haycock (1978)

Body Surface Area Calculator — Answer & Method

Calculate body surface area (BSA) using the Du Bois, Mosteller, and Haycock formulas.

Formula: Du Bois Formula

BSA = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425

H = Height (cm)

W = Weight (kg)

Example Calculation

A person 175 cm tall weighing 75 kg has a BSA of approximately 1.91 m².

Important limitation

This is an educational estimate, not a diagnosis or a substitute for professional medical advice.

Key Facts

Average adult BSA is approximately 1.7 m².
BSA is used in medicine to calculate drug dosages, especially chemotherapy.

Sources & Validation

Du Bois & Du Bois (1916)Mosteller (1987)Haycock (1978)

Related Calculators

BMI Calculator Ideal Weight Calculator

Deterministic: YesAI-Generated Numbers: NoVerified: 2026-02-12

Want to learn more? Browse our calculation guides and tutorials →