| Drug / Action | Dose | Calculated | Notes |
|---|
Paediatric Weight Estimation — Formula Guide
In paediatric emergencies, accurate weight measurement is frequently impossible — the child may be unconscious, in respiratory distress, or brought in without a carer who knows their weight. Estimated weight is used to calculate drug doses, fluid volumes, defibrillation energies, and equipment sizes. Multiple validated formulas exist, each with different performance across age ranges.
APLS (6–12 yrs): Weight (kg) = 3 × Age
Luscombe-Owens (1–10 yrs): Weight (kg) = 3 × Age + 7
Nelson (<1 yr): Weight (kg) = (Age months + 9) / 2
Nelson (1–6 yrs): Weight (kg) = Age × 2 + 8
Nelson (7–12 yrs): Weight (kg) = Age × 7/2 - 1
Broselow (by length): Length-based colour-coded zones
APLS Formula — Most Widely Used in the UK and India
The Advanced Paediatric Life Support (APLS) formula is the most commonly used in UK, Australian, and many Asian emergency departments. It uses two simple age-based formulas: 2 × (Age + 4) for children aged 1–5 years, and 3 × Age for children aged 6–12 years. It is easy to calculate mentally in an emergency. However, APLS tends to underestimate weight in children from higher-income countries and overweight children — several studies have documented APLS underestimating weight by 10–20% in modern paediatric populations.
Luscombe-Owens Formula — Better Accuracy in Overweight Children
The Luscombe-Owens formula (Weight = 3 × Age + 7) was published in 2007 specifically to address the systematic underestimation of APLS in contemporary children. Multiple validation studies across UK, Australia, India, and Southeast Asia have shown Luscombe-Owens provides better mean weight estimates across most age groups from 1–10 years and is now recommended by many paediatric emergency societies as an alternative to APLS. For children above the 50th centile for their age, Luscombe-Owens is the preferred formula.
Broselow Tape — The Gold Standard for Length-Based Estimation
The Broselow Paediatric Emergency Tape is a length-based colour-coded resuscitation tool that estimates weight and provides pre-calculated drug doses and equipment sizes for children up to 36 kg (approximately 12 years). It is the most validated tool in paediatric emergency medicine, with accuracy superior to most age-based formulas. The tape is placed beside the child from head to heel; the colour zone at the heel determines the weight estimate and corresponding pre-calculated doses. The Broselow tape is standard equipment in well-resourced paediatric emergency departments worldwide.
Normal Paediatric Weight Reference Table
| Age | Weight (50th centile) | APLS Estimate | Luscombe-Owens |
|---|---|---|---|
| Newborn | 3.5 kg | — | — |
| 3 months | 6 kg | — | — |
| 6 months | 7.5 kg | — | — |
| 12 months | 10 kg | 10 kg | 10 kg |
| 2 years | 12 kg | 12 kg | 13 kg |
| 5 years | 18 kg | 18 kg | 22 kg |
| 8 years | 25 kg | 24 kg | 31 kg |
| 10 years | 32 kg | 30 kg | 37 kg |
| 12 years | 40 kg | 36 kg | 43 kg |
Key Principles for Emergency Paediatric Drug Dosing
- Always use actual weight when available — these formulas are for emergencies when weighing is impossible or impractical
- Do not exceed adult doses — paediatric drug doses have maximum caps equal to standard adult doses for most drugs
- Double-check every calculation — drug errors are the most common cause of preventable harm in paediatric emergencies
- For obese children — use ideal body weight (IBW) for most weight-based drugs. Use actual weight for adrenaline/epinephrine in anaphylaxis and defibrillation
- Adrenaline in cardiac arrest — 0.1 mg/kg IV/IO (1:10,000 solution = 0.1 mL/kg). Maximum single dose 1 mg
- Defibrillation — 4 J/kg for first shock (AHA/ILCOR 2020). Subsequent shocks 4 J/kg. Maximum 360 J (monophasic) or 200 J (biphasic)