Dubois Formula Calculator: BSA Explained

The Dubois formula calculator estimates body surface area (BSA) in square meters using just weight and height. You enter your weight in kilograms and height in centimeters, and the calculator returns your estimated BSA, which is a key value used in medical dosing and physiological assessments.

Formula

The Dubois formula is written as:

BSA (m²) = 0.007184 × Weight (kg)^0.425 × Height (cm)^0.725

Where:

• BSA = body surface area in square meters (m²)
• Weight = body mass in kilograms (kg)
• Height = standing height in centimeters (cm)

The constants 0.007184, 0.425, and 0.725 were derived by Du Bois and Du Bois in 1916 from a small sample of nine individuals. Despite its age, it remains one of the most widely used BSA formulas in clinical practice.

Worked Example

Using the default values from the calculator (weight = 70 kg, height = 170 cm):

1. Weight^0.425 = 70^0.425 ≈ 6.057
2. Height^0.725 = 170^0.725 ≈ 41.06
3. Multiply: 6.057 × 41.06 ≈ 248.7
4. Multiply by 0.007184: 248.7 × 0.007184 ≈ 1.79 m²

The calculator displays 1.79 m², matching the manual calculation.

Why BSA Matters

Body surface area is used in medicine for several reasons:

• Chemotherapy dosing: Many cytotoxic drugs are dosed per m² of BSA to reduce inter-patient variability.
• Cardiac output indexing: Cardiac index (CI) is cardiac output divided by BSA, normalizing for body size.
• Renal function: Glomerular filtration rate (GFR) is often reported per 1.73 m² of BSA.
• Physiological comparisons: Basal metabolic rate and oxygen consumption are sometimes expressed per m².

Using BSA instead of weight alone helps account for both height and weight, making doses more individualized.

How to Choose Between BSA Formulas

The Dubois formula is not the only BSA estimator. Common alternatives include:

• Mosteller formula: BSA = sqrt( (height (cm) × weight (kg)) / 3600 ). Simpler and nearly as accurate for adults.
• Haycock formula: BSA = 0.024265 × weight^0.5378 × height^0.3964. Often used for children and infants.
• Gehan and George formula: BSA = 0.0235 × weight^0.51456 × height^0.42246. Developed from a larger dataset.

For most adults, the Dubois and Mosteller formulas agree within 1–2%. The Dubois formula tends to slightly underestimate BSA in obese individuals and overestimate in very tall or very short people. If you are using BSA for a critical medical decision, ask your clinician which formula they prefer.

Common Mistakes and Limitations

When using the Dubois formula, watch out for these pitfalls:

• Unit mix-ups: The formula requires weight in kg and height in cm. If you enter pounds or inches, the result will be wrong. Convert first: 1 lb = 0.4536 kg, 1 inch = 2.54 cm.
• Rounding too early: Rounding intermediate values can change the final BSA by 0.02–0.05 m², which may matter for drug dosing.
• Using for children: The Dubois formula was derived from adults; for children under 5 years, other formulas like Haycock are more accurate.
• Extreme body shapes: The formula is less accurate for amputees, severely edematous patients, or those with unusual body proportions.

Also note that the formula does not account for age, sex, or body composition. Two people with the same height and weight will have the same BSA, even if one is muscular and the other is obese.

How to Read the Result

The result is a single number in square meters. Typical adult BSA ranges from about 1.5 to 2.2 m². A value below 1.0 m² is seen in small children, and above 2.5 m² is rare in adults. The number itself is not a health score; it is a scaling factor. For example, if a chemotherapy drug is dosed at 100 mg/m², a patient with a BSA of 1.79 m² would receive 179 mg. Always confirm the dose with a healthcare professional.

Practical Applications and Context

Beyond clinical use, BSA is used in sports science to estimate metabolic rate and in physiology labs to normalize measurements. Some medical calculators use BSA to adjust drug doses for patients with liver or kidney disease. Because the Dubois formula is over a century old, many institutions now use the Mosteller formula for its simplicity, but the Dubois formula remains a standard reference in pharmacology textbooks.

Frequently Asked Questions

Is the Dubois formula the same as the Mosteller formula?

No. Mosteller uses a square root: BSA = sqrt( (height × weight) / 3600 ). Dubois uses exponents. For a typical adult (170 cm, 70 kg), Dubois gives 1.79 m², Mosteller gives 1.82 m² – about 2% difference. Both are acceptable in most clinical contexts.

Can I use the Dubois formula for children?

It is not recommended for children under 5 years. The formula was derived from adult data. For children, the Haycock or Mosteller formulas are often used, but always follow pediatric-specific guidelines.

What units do I need to enter?

Weight must be in kilograms and height in centimeters. If you measure weight in pounds, divide by 2.2046 to get kg. If height is in inches, multiply by 2.54 to get cm.

Why does my BSA matter for medication dosing?

Many drugs, especially chemotherapy agents, are dosed per square meter of body surface area. This is because BSA correlates better with drug clearance than weight alone for certain medications. Your doctor calculates your BSA to determine the exact dose you should receive.

Is a higher BSA always a bad thing?

No. BSA is just a body size measurement. A taller or heavier person will have a higher BSA. It is not a direct indicator of health. However, a very high BSA may affect drug dosing and the interpretation of tests like cardiac output.

Does the Dubois formula work for obese patients?

It tends to underestimate BSA in obese individuals because the formula was derived from people with normal body proportions. For obese patients, some clinicians prefer the Mosteller formula or a direct measurement method. Discuss with your healthcare provider if you have concerns.

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in w | Weight | kg | 70 | 0
in h | Height | cm | 170 | 0
out bsa | Body surface area | m² | 0.007184 * (w^0.425) * (h^0.725) | 2