What it is
When a sick or injured child arrives and weight cannot be measured, almost every weight-based decision — drug doses, fluid boluses, defibrillation energy, tube sizes — needs a number now. APLS age-based formulae give a quick estimate from age alone. They are a stopgap; a measured weight or a length-based tool is always preferable.
The formulae
The current APLS set uses three age bands:
| Age band | Formula |
|---|---|
| 0–12 months | weight (kg) = (0.5 × age in months) + 4 |
| 1–5 years | weight (kg) = (2 × age in years) + 8 |
| 6–12 years | weight (kg) = (3 × age in years) + 7 |
The 6–12 year formula is the Luscombe and Owens equation, adopted because the older “(age × 2) + 8” rule increasingly under-estimated weight in heavier modern children.
When to use it
In any pediatric resuscitation or emergency where the child cannot be weighed and no caregiver-reported recent weight is available. Reach for it for the first dose/bolus while you obtain something better.
Worked example
A 4-year-old in status epilepticus, no scales to hand:
- Band 1–5 years → weight = (2 × 4) + 8 = 16 kg.
- That 16 kg then drives the benzodiazepine dose, fluid bolus (20 mL/kg = 320 mL), and so on — recalculated the moment a real weight appears.
Pitfalls and caveats
- Mind the units. The infant formula uses months; the child formulae use years. Mixing them up is a classic, dangerous slip.
- Population-dependent accuracy. These formulae were validated largely in well-nourished Western cohorts. In under-nourished populations they over-estimate (risking overdose); in populations with high childhood obesity they may under-estimate. Local validation matters.
- A length-based tool beats age. The Broselow tape (or PAWPER) uses length ± habitus and is generally more accurate than any age formula — use it if you have one.
- Replace it immediately. The estimate is for the first few minutes only; substitute a measured weight as soon as practicable and recompute critical doses.
Run it: Estimated Weight for Age (APLS)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.