Which formula is most accurate?

The Luscombe-Owens formula (3 × age + 7) has been shown in multiple studies to be more accurate than the original APLS formula (2 × [age + 4]), which tends to underestimate weight in older or heavier children. For infants the (age in months + 9) / 2 formula provides a rough estimate.

At what ages do these formulas apply?

The age-based formulas are validated for children aged 1 to 10 years. For infants under 12 months the simplified infant formula is used. Above 10 years the estimates become less reliable because of variable pubertal growth; a measured weight is strongly preferred.

Should I use this tool instead of weighing the child?

No. A measured weight is always preferred when time and equipment allow. These formulas are intended for situations where weighing is not immediately possible, such as during resuscitation. Always recheck dosing against an actual weight as soon as one is available.

What is the APLS formula?

APLS stands for Advanced Paediatric Life Support. This tool displays the classic formula: weight (kg) = 2 × (age in years + 4), for children aged 1–10 years.

What is the Luscombe-Owens formula?

The Luscombe-Owens formula, published in 2007, estimates weight as: weight (kg) = (3 × age in years) + 7. It was derived from a large UK dataset and was shown to be more accurate than the original APLS formula across most age groups.

How does the Broselow tape relate to these formulas?

The Broselow tape estimates weight from measured body length, not age. The age-to-weight formulas are complementary — useful when length cannot be measured quickly. Both approaches give estimates in the same general range for most children.

Pediatric Weight Estimation

Enter a child's age to estimate weight in kg using APLS Classic and Luscombe-Owens formulas for emergency dosing.

Patient Age

Age (months)

Enter 0–11 months for the infant formula.

Formula Reference

1. APLS Classic (1–10 yr): 2 × (age + 4)
2. Luscombe-Owens (1–10 yr): 3 × age + 7
3. Infant formula (<12 mo): (months + 9) / 2

All estimates in kilograms. For clinical use only when a scale is unavailable.

Enter the child's age on the left to see weight estimates.

Age: — —

Estimated weight range across all formulas:

— kg

Quick Reference — Common Ages

Age	APLS Classic	Luscombe-Owens

Clinical note: These are estimates only. Always use a measured weight when available. Formulas are validated for ages 1–10 years; accuracy decreases outside this range.

Summary

This tool estimates a child's weight from age alone using APLS Classic, Luscombe-Owens, and an infant formula. When a scale is unavailable during a pediatric emergency, these estimates can support initial medication and equipment checks until a measured weight is available.

How it works

Enter the child's age in years and months (or months only for infants).
Select whether the child is an infant (under 12 months) or older child.
The APLS classic formula (2 × [age + 4]) is applied for children 1–10 years.
The Luscombe-Owens formula (3 × age + 7) is applied for children 1–10 years.
For infants under 12 months the weight is estimated as (age in months + 9) / 2.
The age-appropriate estimates are shown alongside a reference range for quick comparison.

Use cases

Rapidly estimate weight for emergency drug dosing when a scale is unavailable.
Pre-calculate resuscitation fluid volumes before a pediatric code.
Select appropriate endotracheal tube size and equipment during intubation.
Support pre-hospital providers making weight-based dosing decisions in the field.
Teach medical students and residents the standard pediatric weight formulas.
Cross-check a parent-reported weight before administering high-risk medications.
Estimate weight for triage screening when a child's weight history is unavailable.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu