Body Surface Area (BSA) Calculator

Calculate body surface area using multiple formulas. Essential tool for medical dosage calculations and clinical assessments.

Metric System (kg, cm)
Imperial System (lb, in)
kg
Enter weight in kilograms
1 kg 70 kg 300 kg
cm
Enter height in centimeters
50 cm 170 cm 250 cm
years
Patient age in years (affects some BSA formulas)
Calculating...

Understanding Body Surface Area (BSA)

Body Surface Area (BSA) is the calculated surface area of a human body. It is used in many medical settings to calculate drug dosages, cardiac index, and other physiological measurements that need to be normalized by body size.

Clinical Importance: BSA is considered a more accurate indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass. This makes it particularly useful for calculating drug dosages for chemotherapy, antimicrobials, and other medications with narrow therapeutic windows.

BSA Calculation Formulas

Most Common BSA Formulas:
1. Du Bois & Du Bois: BSA = 0.007184 × Weight0.425 × Height0.725
2. Mosteller: BSA = √(Weight × Height / 3600)
3. Haycock: BSA = 0.024265 × Weight0.5378 × Height0.3964
4. Gehan & George: BSA = 0.0235 × Weight0.51456 × Height0.42246
5. Boyd: BSA = 0.0003207 × Weight(0.7285 - 0.0188 × log(Weight)) × Height0.3
Formula Year Common Use Accuracy
Du Bois & Du Bois 1916 Standard reference, clinical research High for adults
Mosteller 1987 Clinical practice, easy calculation High, simplified
Haycock 1978 Pediatrics, all ages High for children
Gehan & George 1970 Chemotherapy dosing High for drug dosing
Boyd 1935 Historical, comprehensive Good for wide ranges

Clinical Applications of BSA

Drug Dosage Calculation
Chemotherapy, antimicrobials, cardiovascular drugs, and other medications with narrow therapeutic windows are often dosed based on BSA.
Cardiac Index
Cardiac output is often indexed to BSA to create the cardiac index, which allows comparison between individuals of different sizes.
Glomerular Filtration Rate
GFR is often adjusted for BSA to account for differences in body size when assessing kidney function.
Metabolic Rate
Basal metabolic rate correlates better with BSA than with weight, making it useful in nutritional assessments.
Fluid Requirements
In burn patients, fluid resuscitation is often calculated based on BSA affected by burns (Parkland formula).
Dosing in Obesity
For obese patients, BSA-based dosing is often preferred over weight-based dosing to avoid overdosing.

Normal BSA Ranges by Age and Gender

Age Group Male (m²) Female (m²) Clinical Notes
Newborn 0.2 - 0.3 0.2 - 0.3 Rapid increase in first year
1 year 0.4 - 0.5 0.4 - 0.5 Doubles from birth to 1 year
5 years 0.7 - 0.8 0.7 - 0.8 Pediatric formulas preferred
10 years 1.0 - 1.2 1.0 - 1.2 Gender differences emerge
Adult 1.7 - 2.0 1.6 - 1.9 Most common reference range
Elderly 1.6 - 1.9 1.5 - 1.8 Decreases with age due to height loss

BSA in Special Populations

1

Pediatric Patients: BSA is particularly important in children as drug metabolism and distribution differ significantly from adults. The Haycock formula is often preferred for pediatric calculations.

2

Obese Patients: BSA-based dosing is often more accurate than weight-based dosing for obese individuals, as it accounts for increased metabolic mass without overestimating drug requirements.

3

Elderly Patients: Age-related changes in body composition and organ function may require BSA-adjusted dosing, especially for renally excreted drugs.

4

Burn Patients: The extent of burns is measured as a percentage of total BSA, and fluid resuscitation is calculated based on burned BSA.

Clinical Note: While BSA is a valuable tool for individualizing drug therapy, it should always be used in conjunction with clinical judgment. Other factors such as organ function, age, comorbidities, and drug-specific pharmacokinetics must also be considered when determining appropriate dosages.

Frequently Asked Questions

BSA correlates better with metabolic processes and organ size than body weight alone. This is particularly important for drugs with narrow therapeutic windows, like chemotherapy agents, where precise dosing is critical. BSA accounts for differences in body composition and is less affected by adipose tissue, which has lower metabolic activity compared to lean body mass.

The Mosteller formula is widely accepted as accurate and easy to calculate. The Du Bois formula is historically the standard reference. For pediatric patients, the Haycock formula is often preferred. The choice of formula may depend on institutional protocols, the specific drug being administered, and patient characteristics. In practice, different formulas typically yield similar results for most adult patients.

BSA increases rapidly during childhood, doubling from birth to 1 year and continuing to increase throughout childhood and adolescence. It peaks in early adulthood and then gradually declines in older age due to decreases in height (from spinal compression) and changes in body composition. This is why age-adjusted formulas or pediatric-specific formulas are important for accurate calculations in children.

BSA should not be used for drugs that are primarily distributed in body water (use lean body weight), for drugs with significant central nervous system penetration, or for extremely underweight or cachectic patients. Some drugs have specific dosing guidelines that override BSA-based calculations. Always follow drug-specific prescribing information and consult with clinical pharmacists when in doubt.

In burn medicine, the "Rule of Nines" is used to estimate the percentage of total BSA affected by burns. This assessment guides fluid resuscitation using formulas like the Parkland formula, which calculates fluid requirements based on burned BSA percentage and patient weight. Accurate BSA estimation is critical in burn management to prevent both under-resuscitation and fluid overload.