BSA Calculator: Calculate Body Surface Area

An expert tool for finding Body Surface Area (BSA) using multiple standard formulas from height and weight.

Comparison of BSA Formulas

Formula Name	Calculated BSA (m²)
Mosteller	1.87
Du Bois	1.85
Haycock	1.86
Gehan & George	1.85

What are formulas using height and weight to calculate BSA?

Body Surface Area (BSA) is the total surface area of the human body. For many clinical purposes, BSA is considered a better indicator of metabolic mass than simple body weight because it is less affected by abnormal adipose (fat) mass. Therefore, understanding the formulas using height and weight to calculate BSA is crucial in medical fields. These calculations are widely used to determine dosages for medications with a narrow therapeutic index, such as chemotherapy drugs, where precision is critical to maximize effectiveness and minimize toxicity.

While direct measurement is impractical, several mathematical formulas have been developed over the last century to estimate BSA accurately. These formulas typically require only a person’s height and weight as inputs, making them easy to use in any clinical setting. This calculator provides results from four of the most recognized and validated formulas. You can learn more about how to calculate your ideal body weight as a related health metric.

BSA Formula and Explanation

There isn’t one single formula for BSA, but rather several that are used in different contexts. This calculator computes BSA using four common estimation formulas.

Common BSA Formulas

• Mosteller Formula: BSA (m²) = √((Height(cm) * Weight(kg)) / 3600). [1] This is the most widely used formula today due to its simplicity and reliable accuracy across different body types.
• Du Bois Formula: BSA (m²) = 0.007184 * Height(cm)^0.725 * Weight(kg)^0.425. [14] One of the oldest and most extensively validated formulas, it remains a cornerstone in clinical practice.
• Haycock Formula: BSA (m²) = 0.024265 * Height(cm)^0.3964 * Weight(kg)^0.5378. [18] This formula was specifically developed and validated for use in infants and children, but is also accurate for adults.
• Gehan and George Formula: BSA (m²) = 0.0235 * Height(cm)^0.42246 * Weight(kg)^0.51456. [19] Developed from a large study, it provides another reliable estimation.

Variables Used in BSA Formulas

Variable	Meaning	Unit	Typical Range
BSA	Body Surface Area	m² (square meters)	1.5 – 2.2 m² (for adults)
Weight (W)	Patient’s body mass	kg (kilograms) or lbs (pounds)	40 – 150 kg
Height (H)	Patient’s stature	cm (centimeters) or in (inches)	140 – 210 cm

Practical Examples

Example 1: Metric Units

Let’s calculate the BSA for an adult male using metric units.

• Input – Weight: 80 kg
• Input – Height: 180 cm
• Using the Mosteller Formula: BSA = √((180 * 80) / 3600) = √(14400 / 3600) = √4 = 2.0 m²
• Result: The individual’s Body Surface Area is approximately 2.0 m².

Example 2: Imperial Units

Now let’s calculate the BSA for an adult female using imperial units.

• Input – Weight: 150 lbs
• Input – Height: 66 inches
• Conversion to Metric: 150 lbs ≈ 68.04 kg; 66 inches = 167.64 cm
• Using the Mosteller Formula: BSA = √((167.64 * 68.04) / 3600) = √(11406.2) / 3600) = √3.168 = 1.78 m²
• Result: The individual’s Body Surface Area is approximately 1.78 m². Our calculator handles this conversion automatically when you select the imperial unit system. For other health calculations, you might find a basal metabolic rate calculator useful.

How to Use This BSA Calculator

Using this calculator to determine BSA with various formulas using height and weight to calculate bsa is straightforward. Follow these steps:

1. Select Unit System: First, choose between ‘Metric (kg, cm)’ or ‘Imperial (lbs, in)’ from the dropdown menu. The input labels will update automatically.
2. Enter Weight: Input the person’s weight into the corresponding field.
3. Enter Height: Input the person’s height.
4. Review Results: The calculator instantly updates. The primary result box shows the BSA calculated with the recommended Mosteller formula. The table below compares this value with results from the Du Bois, Haycock, and Gehan & George formulas. The bar chart provides a quick visual comparison.
5. Reset or Copy: Use the ‘Reset’ button to return to the default values or the ‘Copy Results’ button to copy a summary to your clipboard.

Key Factors That Affect Body Surface Area

Several factors influence an individual’s BSA. While height and weight are the direct inputs for the formulas, other intrinsic factors determine those measurements.

• Height: A taller person will have a larger BSA than a shorter person of the same weight.
• Weight: A heavier person will have a larger BSA than a lighter person of the same height.
• Body Composition: While formulas don’t directly account for it, body composition (muscle vs. fat) influences weight. Two people of the same height and weight can have different body shapes, but their calculated BSA will be the same.
• Age: BSA changes significantly from infancy to adulthood. Children have a much higher surface-area-to-volume ratio. Many use specific calculators for this, like a child BMI calculator.
• Sex: On average, adult males have a larger BSA than adult females due to average differences in height and weight.
• Extreme Body Types: For individuals who are extremely obese or lean, some formulas may be more accurate than others. The Du Bois formula, for example, has been shown to be effective across a wide range of body types.

Frequently Asked Questions (FAQ)

Why are there so many different formulas to calculate BSA?

Each formula was developed using different subject populations and statistical methods. The Mosteller formula is popular for its simplicity, while others like Haycock were specifically validated for pediatric use. [6] Having multiple formulas allows clinicians to choose the one best suited for their patient population.

Which BSA formula is the most accurate?

The Mosteller formula is widely considered the best for routine clinical use due to its balance of simplicity and accuracy. [1] However, for specific populations like infants, other formulas like Haycock might be preferred.

What is a normal BSA for an adult?

The average BSA for an adult male is around 1.9 m² and for an adult female is around 1.6 m². However, this can vary widely based on individual height and weight.

How is BSA different from BMI?

Body Mass Index (BMI) is a measure of body fat based on weight relative to height (kg/m²). BSA is a measure of total body surface area (m²). BSA is often considered a better indicator of metabolic rate and is preferred for certain medical calculations, like chemotherapy dosing. You can compare your results with a standard BMI calculator.

Why is BSA important for chemotherapy?

Many chemotherapy drug dosages are based on BSA. This method is believed to provide a more consistent drug exposure across patients of different sizes compared to dosing based on weight alone, helping to balance efficacy and toxicity. [9]

How do I measure my height and weight accurately?

For best results, measure weight in the morning before eating and after emptying your bladder, wearing minimal clothing. Measure height without shoes, standing straight against a wall.

Can I use this calculator for a child?

Yes, the formulas provided, particularly Haycock and Gehan & George, are validated for use in children. However, always consult a pediatrician for medical decisions regarding children.

Does changing the unit system affect the result?

No. The calculator automatically converts imperial units (pounds, inches) to metric units (kg, cm) internally before applying the formulas. The final BSA result is always displayed in square meters (m²) for consistency.