Body Surface Area Calculator

What is Body Surface Area Calculator?

The Body Surface Area (BSA) Calculator is a medical tool that estimates the total surface area of the human body based on height and weight. BSA is a crucial metric in healthcare used for calculating appropriate medication dosages (especially chemotherapy), determining cardiac index, assessing burn severity, calculating proper dialysis doses, and other clinical applications.

This calculator uses multiple validated formulas including Du Bois & Du Bois (1916), Mosteller (1987), Haycock (1978), and Gehan & George (1970). Each formula has been validated through extensive clinical research and is used in different medical contexts. The average human BSA is approximately 1.7-1.9 m² for adults.

BSA is more accurate than body weight alone for medical calculations because it better correlates with metabolic mass and physiological parameters. It accounts for both height and weight, providing a more comprehensive assessment of body size.

How to Use This Tool

Step 1: Choose Weight Unit

Select your preferred measurement system:

Available Units:

• Kilograms (kg): Metric system, standard in most countries
• Pounds (lbs): Imperial system, common in United States

Common Usage:

• Medical settings worldwide use kilograms
• Hospital records typically in kg
• Research studies use metric
• US patients often know weight in lbs

Conversion:

• 1 kg = 2.20462 lbs
• 1 lb = 0.453592 kg
• Calculator converts automatically
• Both units give identical BSA result

Step 2: Enter Your Weight

Input your current body weight:

What to Enter:

• Current weight in selected unit
• Can include decimals (e.g., 70.5 kg)
• Must be realistic adult weight
• Use most recent accurate measurement

Measuring Weight:

• Use calibrated scale
• Weigh in morning before eating
• Minimal clothing for accuracy
• Hospital scales most accurate
• Remove shoes and heavy items

Weight Tips:

• Medical dosing requires accuracy
• Recent measurement preferred (within 1 month)
• Significant weight changes affect BSA
• Pregnant women: use pre-pregnancy weight unless specified
• Amputees: special formulas may be needed

Typical Adult Ranges:

• Men: 60-100 kg (132-220 lbs)
• Women: 50-85 kg (110-187 lbs)
• Athletes may be higher (muscle mass)
• Elderly may be lower

Step 3: Choose Height Unit

Select your preferred measurement system:

Available Units:

• Centimeters (cm): Metric, single input
• Feet & Inches: Imperial, two inputs

Common Usage:

• Most countries use centimeters
• United States uses feet and inches
• Medical records may use either
• International studies use metric

Input Methods:

• Centimeters: Single number (e.g., 175)
• Feet & Inches: Two fields (e.g., 5 feet, 9 inches)
• Calculator handles conversion
• Results identical either way

Step 4: Enter Your Height

Input your height in selected unit:

If Using Centimeters:

• Enter total height in cm
• Can include decimals (e.g., 175.5)
• Typical adult range: 150-200 cm
• Example: 175 cm

If Using Feet & Inches:

• Feet field: Whole feet (4-7 typically)
• Inches field: Remaining inches (0-11)
• Example: 5 feet, 9 inches
• Don't enter total inches in feet field

Measuring Height:

• Remove shoes
• Stand straight against wall
• Heels together, looking forward
• Mark wall at top of head
• Measure from floor to mark
• Medical office measurements most accurate

Height Tips:

• Height remains stable in adults
• Morning height slightly taller (spine compression during day)
• Elderly may have height loss (osteoporosis)
• Accurate measurement critical for BSA
• Use most recent doctor measurement if available

Typical Adult Ranges:

• Men: 165-185 cm (5'5"-6'1")
• Women: 155-175 cm (5'1"-5'9")
• Significant variation by ethnicity
• Individual variation normal

Step 5: Select BSA Formula

Choose the calculation method:

Available Formulas:

Du Bois & Du Bois (1916):

• Most widely used formula
• Oldest validated formula (over 100 years)
• Extensive clinical validation
• Standard in many medical contexts
• Good for general population
• Formula: BSA = 0.007184 × W^0.425 × H^0.725

Mosteller (1987):

• Simplest formula
• Easiest to calculate manually
• Very accurate for average adults
• Often used in oncology
• Recommended by FDA for some applications
• Formula: BSA = √(H × W / 3600)

Haycock (1978):

• Developed for children
• Also accurate for adults
• Good for pediatric oncology
• Wide age range validation
• Formula: BSA = 0.024265 × W^0.5378 × H^0.3964

Gehan & George (1970):

• Validated for cancer patients
• Used in chemotherapy dosing
• Good for wider weight ranges
• Common in oncology
• Formula: BSA = 0.0235 × W^0.51456 × H^0.42246

Which Formula to Choose:

• General use: Du Bois (most common)
• Quick calculation: Mosteller
• Chemotherapy: Gehan & George or Mosteller
• Children: Haycock
• Obesity: Gehan & George
• When unsure: Compare all (differences usually <5%)

Step 6: Calculate BSA

Click Calculate to see results:

What the Calculator Does:

• Converts units if needed
• Applies selected formula
• Calculates BSA in square meters (m²)
• Shows comparison with all formulas
• Provides clinical context

BSA Result:

• Displayed in m² (square meters)
• Typically 1.5-2.5 m² for adults
• Two decimal places precision
• Used for medical calculations

Understanding Your Result:

Average Adult BSA:

• Men: 1.9 m² (range 1.7-2.1 m²)
• Women: 1.6 m² (range 1.5-1.8 m²)
• Children: 0.5-1.5 m² (age dependent)
• Newborns: ~0.25 m²

Clinical Ranges:

• Very small adult: <1.5 m²
• Small adult: 1.5-1.7 m²
• Average adult: 1.7-2.0 m²
• Large adult: 2.0-2.3 m²
• Very large adult: >2.3 m²

Step 7: Review All Formula Results

Compare results across formulas:

Why Compare:

• See consistency across methods
• Identify any unusual variations
• Understand range of values
• Choose most appropriate for context

Expected Differences:

• Usually within 5% of each other
• Larger differences if unusual body proportions
• Very tall/short may show more variation
• Obesity may affect formulas differently

When Results Differ Significantly:

• Check inputs for errors
• Verify height and weight accurate
• Consider unusual body proportions
• Consult healthcare provider
• They can determine best formula

Step 8: Understand Clinical Applications

Learn how BSA is used medically:

Medication Dosing:

• Chemotherapy doses calculated by BSA
• More accurate than weight alone
• Reduces toxicity risk
• Standard oncology practice
• Formula: Dose = BSA × dose per m²

Cardiac Index:

• Cardiac output adjusted for body size
• CI = Cardiac Output ÷ BSA
• Normal CI: 2.5-4.0 L/min/m²
• Critical care monitoring
• Heart function assessment

Burn Assessment:

• Burn percentage calculation
• Fluid resuscitation formulas
• Rule of Nines uses BSA
• Critical for burn treatment
• Survival prediction

Renal Function:

• GFR normalization
• Dialysis dose calculation
• Kidney function assessment
• Dosing of renal-cleared drugs

Other Applications:

• Radiation therapy planning
• Metabolic rate estimation
• Pediatric dosing
• Clinical research
• Physiological studies

Step 9: Document Your BSA

Record for medical purposes:

What to Record:

• BSA value (m²)
• Formula used
• Date calculated
• Height and weight used
• Purpose of calculation

Why Document:

• Medical records consistency
• Track changes over time
• Medication dosing reference
• Share with healthcare team
• Emergency information

When to Recalculate:

• Significant weight change (>5 kg / 10 lbs)
• Before chemotherapy cycles
• Medication dose adjustments
• Major illness or surgery
• Pregnancy (as directed)
• Every 3-6 months if stable

Step 10: Consult Healthcare Provider

Discuss results with medical team:

Important:

• BSA calculator is informational
• Not a substitute for medical advice
• Doctor determines medication doses
• Clinical context essential
• Other factors considered

Questions to Ask:

• Which formula should I use?
• How does my BSA affect treatment?
• Should I recalculate regularly?
• Any concerns about my BSA?
• How does this affect my medication?

Medical Considerations:

• Obesity may affect formula accuracy
• Amputations require adjustments
• Edema can affect weight measurement
• Pregnancy changes BSA
• Age affects interpretation

Understanding Body Surface Area

Why BSA Matters in Medicine

More Accurate Than Weight:

• Correlates better with metabolic mass
• Accounts for both height and weight
• Reduces dosing errors
• Standard in clinical practice
• Improves treatment outcomes

Physiological Basis:

• Body functions scale with surface area
• Heat loss related to BSA
• Metabolic rate proportional to BSA
• Organ function correlates with BSA
• Better than weight for size adjustment

Historical Development:

• First formulas in early 1900s
• Extensive research and validation
• Multiple formulas for different populations
• Continuously refined
• Globally accepted standard

Factors Affecting BSA

Body Composition:

• Muscle mass increases BSA
• Obesity affects calculations
• Very lean or muscular bodies
• Different formulas may vary more

Age:

• Children have lower BSA
• Grows with development
• Peaks in young adulthood
• May decrease with aging
• Pediatric formulas available

Gender:

• Men typically higher BSA (larger on average)
• Women typically lower BSA
• Accounts for size differences
• Not used to adjust formula
• Same formulas for both genders

Ethnicity:

• Average heights vary
• Different body proportions
• Formulas validated across populations
• Same calculations apply
• Individual variation more significant

Medical Conditions:

• Amputations reduce BSA
• Edema falsely increases weight
• Cachexia decreases BSA
• Obesity increases BSA
• Special considerations needed

Frequently Asked Questions

Q1: What is body surface area and why is it important?

Short Answer: Body surface area (BSA) is the total surface area of the human body measured in square meters (m²). It's crucial in medicine for calculating appropriate medication doses, especially chemotherapy, because it correlates better with metabolic mass than body weight alone.

What BSA Represents:

• Total outer surface of body
• Measured in square meters (m²)
• Calculated from height and weight
• Cannot be measured directly
• Estimated using validated formulas

Why It's Important:

• More accurate than weight for dosing
• Accounts for body size comprehensively
• Correlates with metabolic activity
• Standard in clinical practice worldwide
• Improves medication safety

Medical Applications:

• Chemotherapy dosing (most cancer drugs dosed by BSA)
• Cardiac index calculation
• Burn treatment (fluid resuscitation)
• Dialysis dosing
• Radiation therapy planning
• Pediatric medication dosing

Typical BSA Values:

• Average adult man: 1.9 m²
• Average adult woman: 1.6 m²
• Range: 1.5-2.3 m² for adults
• Children: 0.5-1.5 m²
• Newborns: ~0.25 m²

Q2: Which BSA formula is most accurate?

Short Answer: All four formulas (Du Bois, Mosteller, Haycock, Gehan & George) are scientifically validated and usually give results within 5% of each other. Du Bois is most widely used historically, while Mosteller is simplest and often preferred for adults.

Du Bois & Du Bois (1916):

• Most widely used, extensively validated
• Historical standard, good for general population
• Complex calculation
• Best for: General medical use, standard reference

Mosteller (1987):

• Simplest formula, easy manual calculation
• Very accurate for average adults
• FDA recommended for some drugs
• Best for: Quick calculations, general adult use, oncology

Haycock (1978):

• Validated for children
• Accurate across wide age range
• Best for: Children, pediatric oncology

Gehan & George (1970):

• Validated for cancer patients
• Good for obesity, wider weight ranges
• Best for: Chemotherapy, obese patients

Recommendations:

• Don't know which: Use Du Bois (most common)
• Quick estimate: Use Mosteller
• Chemotherapy: Ask oncologist preference
• Children: Use Haycock

Q3: How often should I recalculate my BSA?

Short Answer: Recalculate BSA when weight changes by more than 5 kg (10 lbs), before each chemotherapy cycle if receiving cancer treatment, or every 3-6 months if stable.

For Cancer Patients:

• Before each chemotherapy cycle
• If weight changes by >2 kg (4-5 lbs)
• After significant side effects
• As directed by oncologist

For General Medical Use:

• After weight change >5 kg (10 lbs)
• Before starting new medications
• Every 3-6 months if monitoring
• After major surgery
• After significant illness

When BSA Stays Stable:

• Adults with stable weight
• Can use same BSA for months
• Annual update reasonable

When BSA Changes Quickly:

• Rapid weight loss (cancer, illness)
• Rapid weight gain (obesity, edema)
• Pregnancy and postpartum
• Bariatric surgery

Q4: Can I use BSA to calculate my own medication doses?

Short Answer: No, never calculate or adjust medication doses yourself. BSA is just one factor in dosing - your doctor also considers your kidney/liver function, other medications, medical conditions, and drug-specific factors.

Why Self-Dosing is Dangerous:

• BSA is only one dosing factor
• Organ function affects dosing
• Drug interactions must be considered
• Individual response varies
• Many contraindications exist

Additional Factors Doctors Consider:

• Kidney function (creatinine clearance)
• Liver function (hepatic impairment)
• Other medications (interactions)
• Previous drug reactions
• Concurrent medical conditions
• Age-related changes

What BSA Calculator Is For:

• Understanding your body size metrics
• Educational purposes
• Tracking changes over time
• Discussing with healthcare provider
• General health awareness

Never for:

• Calculating drug doses
• Adjusting prescribed medications
• Making treatment decisions
• Self-prescribing

Q5: Is BSA accurate for obese or very thin individuals?

Short Answer: BSA formulas may be less accurate at extremes of body weight. For obese patients, BSA may overestimate metabolic mass; for very thin patients, it may not fully capture body surface. Doctors often use adjusted calculations in these cases.

Obesity Considerations:

• Standard formulas may overestimate
• Fat tissue less metabolically active
• May lead to overdosing if unadjusted
• Oncologist may cap maximum BSA (e.g., 2.0-2.2 m²)
• May use ideal body weight instead

Underweight/Cachexia:

• Very low BSA values
• May underestimate surface area
• Reduced drug tolerance
• May use minimum BSA threshold

When BSA Most Accurate:

• Normal weight range (BMI 18.5-25)
• Average adult proportions
• Standard body composition

Q6: How does BSA relate to BMI?

Short Answer: BSA (body surface area) and BMI (body mass index) are different measurements - BSA measures total body surface in m² using height and weight, while BMI measures weight relative to height (kg/m²) to categorize underweight/normal/overweight.

Key Differences:

• BSA: Total body surface area (m²)
• BMI: Weight-to-height ratio (kg/m²)
• BSA: For medical dosing, physiological calculations
• BMI: For weight category classification

Which to Use:

• Use BSA for: Medication dosing, cardiac index, burn assessment
• Use BMI for: Weight category, health risk screening
• Both useful, serve different purposes

Q7: Do I need to adjust BSA for amputations or limb differences?

Short Answer: Yes, standard BSA formulas assume intact limbs. Amputations or congenital limb differences reduce actual body surface area. Your healthcare provider can adjust BSA calculations using established correction factors.

Surface Area by Body Part:

• Entire arm: ~9% of total BSA
• Forearm and hand: ~6% of BSA
• Hand alone: ~3% of BSA
• Entire leg: ~18% of total BSA
• Lower leg and foot: ~11% of BSA
• Foot alone: ~7% of BSA

Calculation Method:

• Calculate standard BSA first
• Determine amputation percentage
• Subtract from total BSA
• Use adjusted BSA for dosing

Example:

• Standard BSA: 1.80 m²
• Below-knee amputation: -11%
• Adjusted BSA: 1.80 × 0.89 = 1.60 m²

Q8: Can BSA change over time in adults?

Short Answer: Yes, BSA changes in adults when weight changes significantly, though height remains stable. Weight gain increases BSA; weight loss decreases it. Typical changes: 5 kg weight change = ~0.05-0.10 m² BSA change.

Factors Causing BSA Changes:

• Weight gain → BSA increase
• Weight loss → BSA decrease
• Pregnancy (typical gain: 10-15 kg, BSA may increase 0.10-0.15 m²)
• Aging (muscle loss, may decrease 0.05-0.15 m² over decades)
• Illness (cachexia decreases BSA)

What Stays Stable:

• Height (fixed in adults after age 25)
• Bone structure

When to Recalculate:

• Weight change >5 kg (10 lbs)
• Before chemotherapy cycles
• Every 3-6 months if monitoring
• After major illness
• Pregnancy/postpartum