APLS age-based weight estimate (pediatric)

Estimated body weight in kilograms, chosen by age band. Under 1 year: 0.5 × age in months + 4. 1–5 years: 2 × age + 8. 6–12 years: 3 × age + 7 (Luscombe & Owens, replacing the legacy (age + 4) × 2, which underestimated measured weight by a mean of 18.8%). Age is taken in whole years at the last birthday for the child bands. A single age input converts internally, because the infant formula runs in months, a classic unit trap.

A population point estimate for use only when weighing is impossible. A measured weight is always preferred, and the Broselow tape is the length-based alternative, which needs the tape and the child supine and loses accuracy above ~25 kg. Systematically underestimates in overweight and obese children. Not defined outside 0–12 years, and NOT to be extrapolated to a preterm or low-birth-weight neonate: the infant band is anchored to an average term newborn and returns 4 kg at age 0, which over-estimates a small preterm baby several-fold.

References

Luscombe M, Owens B. Weight estimation in resuscitation: is the current formula still valid? Arch Dis Child. 2007;92(5):412–415.Origin of the 6–12y formula weight = (3 × age) + 7 (derived/validated 1–10y); legacy (age+4)×2 underestimated measured weight by a mean of 18.8% (n=17,244), the reason it was replaced.PMID 17213259 DOI 10.1136/adc.2006.107284
Advanced Life Support Group. Advanced Paediatric Life Support: The Practical Approach. 5th ed. Wiley-Blackwell; 2011. ISBN 978-1-4443-3059-5.Manual that introduced the three age-banded formulas: infant (0.5×months)+4, 1–5y (2×age)+8, 6–12y (3×age)+7.Source
Kelly A-M, Nguyen K, Krieser D. Validation of the Luscombe weight formula for estimating children's weight. Emerg Med Australas. 2011;23(1):59–62.Independent validation of (3×age)+7 for ages 1–10y.PMID 21134132 DOI 10.1111/j.1742-6723.2010.01351.x
Lubitz DS, Seidel JS, Chameides L, et al. A rapid method for estimating weight and resuscitation drug dosages from length in the pediatric age group. Ann Emerg Med. 1988;17(6):576–581.Original Broselow length-based tape — a length-based (not age-based) alternative.PMID 3377285

Reproduction rights

Freely reproducible.The equations (0.5×months)+4, (2×age)+8, (3×age)+7 and the age-band selection are mathematical facts / uncopyrightable methods; coefficients are facts (research §"IP status"). Program name (APLS) referenced factually, not reproduced; no Broselow proprietary zone tables are used.

Independent clinical validation: pending

Two independent clinical validators will be named here once review is complete.

Validator slot open 1

Validator slot open 2

2026-08-10v1.0.0Initial releaseInitial published text.
2026-09-03v1.1.0Formula correctionReads a birthday entered in DAYS as that birthday. Age is stored in years and days convert at 365.25, so a sixth birthday of 2191 days became 5.9986 years and a tenth of 3652 days became 9.9986. Anything that floors or bands on whole years then read the child as a year younger. The conversion now snaps to a whole year when the day count is within one day of one, which is the largest the drift can be: 365.25 averages the leap cycle exactly, so a true birthday is always within 0.75 days of the integer. Ages entered in years or months were already exact and are unchanged, and an age more than a day from a birthday is untouched. Found 2026-09-03 by an independent recompute of every calculator from its published source. On this score that returned 18 kg for a six-year-old whose own row gives 25, a 7 kg error on a figure that seeds weight-based drug and fluid doses.
2026-09-06v1.1.1ClarificationAdded a one-line description for the catalogue card. No rule, threshold or reference changed.

References

Reproduction rights

Other general scores