APLS age-based weight estimate (pediatric)

Estimated body weight in kilograms, chosen by age band. Under 1 year: weight = 0.5 × age in months + 4 (equivalently 6 × age in years + 4). 1–5 years: weight = 2 × age in years + 8. 6–12 years: weight = 3 × age in years + 7 (Luscombe & Owens). Age in years is taken at the last birthday (whole years) for the two child bands. This is a population point estimate for use only when a measured weight cannot be obtained — a directly measured weight is always preferred, and a Broselow length tape is a length-based alternative. Not defined below 0 or above 12 years.

An ESTIMATE, not a measurement or severity score — interpretation is intentionally empty (research: no clinical interpretation/risk bands; the only bands are the age bands that select the formula). A directly measured weight is always preferred; use the estimate only when weighing is impossible. The Broselow length tape (Lubitz 1988, PMID 3377285) is a length-based alternative but needs the physical tape and the child supine, and loses accuracy above ~25 kg. The updated 1–5y band (2×age)+8 is algebraically identical to the legacy APLS (age+4)×2; only the 6–12y band was steepened to (3×age)+7 (Luscombe & Owens 2007, PMID 17213259) because the legacy formula underestimated measured weight by a mean of 18.8% across ages 1–10y — e.g. at 10y the legacy 28 kg vs updated 37 kg (~24% gap). Population-derived formulas carry substantial individual error and systematically UNDERESTIMATE in overweight/obese children; validated range is 0–12 years (do not extrapolate to neonates outside term ranges, adolescents >12y, or adults). Age-unit trap: the infant formula is in months, the child formulas in whole years; this calculator takes a single age input and converts internally. No research values were left unsourced (no [NEEDS SOURCE] carried); the 0–12 year input bounds are engineering input-validity limits, not cited clinical thresholds.