Body surface area (Mosteller)

Body surface area is estimated with the Mosteller (1987) formula: BSA in square metres = the square root of (height in cm × weight in kg ÷ 3600), which is equivalently √(height × weight) ÷ 60. It is a single closed-form expression with no age or sex terms and no interpretation bands. The result is a body-size scalar used as a denominator elsewhere — e.g. drug dosing per m² (mg/m²) and indexed haemodynamic/renal parameters such as cardiac index (L/min/m²). Compute in full floating point and round once at display (precision 2); do not chain rounded intermediates.

No interpretation bands: BSA is a continuous body-size scalar with no published cut-point that stratifies patients, so interpretation is intentionally empty — present the value as a derived body-size estimate and defer any dosing/indexing interpretation to the downstream calculation that consumes it. Estimate only, not a clinical device: Mosteller was validated only against the Du Bois formula (itself fit to 9 adults in 1916), not against direct surface-area measurement; agreement with pediatric-fit estimators (Haycock, Gehan-George) is close but widens at the extremes (neonates, severe obesity), so a platform indexing by BSA should record which formula it uses. The main failure mode is unit transposition (lb↔kg, in↔cm): because BSA scales as sqrt(h·w) a swapped unit yields a wrong-but-plausible number the formula cannot self-detect — unit labels and the range checks are the defense. The height (~30–220 cm) and weight (~0.3–250 kg) bounds are input-validity limits chosen to span the PICU range, NOT clinical limits and not from Mosteller 1987. NEEDS SOURCE (carried from research): a specific head-to-head pediatric accuracy figure vs Haycock/Gehan-George is not asserted here, and any protocol BSA cap for dosing (commonly cited around 2.0–2.2 m²) is a protocol overlay, not part of Mosteller, and lacks a primary numeric source.