Body surface area calculator
Body surface area (BSA) is used for chemotherapy and some antimicrobial doses, for cardiac index and for fluid calculations. Enter weight and height and the calculator shows BSA by Mosteller and Haycock; without height, it uses the simplified weight-only formula.
Enter weight and height to obtain the body surface area with the Mosteller and Haycock formulas. Without height, the calculator uses the simplified weight-only formula.
Mosteller: √(height in cm × weight in kg / 3600). Haycock: 0.024265 × weight^0.5378 × height^0.3964, validated in newborns and infants. Weight-only formula: (4 × weight + 9) / 100 up to 10 kg and (4 × weight + 7) / (weight + 90) above that. Body surface area is used for chemotherapy doses, cardiac index and fluid calculations.
Clinical decision-support tool for use by healthcare professionals. It does not replace clinical judgment or your unit's protocols.
Formulas
Mosteller: BSA = √(height in cm × weight in kg / 3600). Haycock: BSA = 0.024265 × weight^0.5378 × height^0.3964, derived in a population that included newborns and infants, hence preferred in neonatology. Weight-only formula: (4 × weight + 9) / 100 up to 10 kg and (4 × weight + 7) / (weight + 90) above that.
Which to use
Haycock is the best validated in newborns and small infants. Mosteller is the most used in pediatric oncology and in adults for its simplicity. The weight-only formula serves as a quick estimate when height is unavailable; in preterm infants length measurement is imprecise and the weight-only formula may be sufficient.
Example
Term newborn weighing 3.2 kg, 50 cm long. Mosteller: √(50 × 3.2 / 3600) = 0.21 m². Haycock: 0.024265 × 3.2^0.5378 × 50^0.3964 = 0.21 m². Weight-only formula: (4 × 3.2 + 9) / 100 = 0.22 m².
Frequently asked questions
Why does BSA matter in neonatology?
Doses of some drugs, the cardiac index in functional echocardiography and certain fluid-loss estimates are expressed per m² of body surface area, not per kg.
Which formula is best for preterm infants?
Haycock, which was derived including low-birth-weight newborns. When height is uncertain, the weight-only formula gives a close result.
Is the difference between the formulas relevant?
In newborns the difference is usually under 5%. For critical doses, use the formula recommended by the drug’s protocol.
References
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
- Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. J Pediatr. 1978;93(1):62-6.
- Sharkey I, et al. Body surface area estimation in children using weight alone: application in paediatric oncology. Br J Cancer. 2001;85(1):23-8.
