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 (1–5 yrs): Weight (kg) = 2 × (Age + 4)
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.
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)
2 Frequently Asked Questions
What is the APLS formula for paediatric weight estimation?
For children 1–10 years: Weight (kg) = 2 × (Age in years + 4). Example: 6-year-old = 2 × (6+4) = 20 kg. Alternative APLS formula: Weight = (Age + 4) × 2. For infants 3–12 months: Weight (kg) = (Age in months + 9) / 2. These are emergency estimates — actual weight should be measured when possible.
Why is accurate weight estimation important in children?
Paediatric drug doses, IV fluid rates, resuscitation drug doses (adrenaline 0.01 mg/kg), defibrillation energy (4 J/kg), endotracheal tube size (age/4 + 4 mm), and tidal volume settings on ventilator are all weight-based. An error of 20% in weight estimation can mean a 20% drug dose error — potentially fatal for high-alert drugs like adrenaline, potassium, or suxamethonium.
What other methods estimate paediatric weight?
Broselow tape: colour-coded tape based on child's height correlates to weight — most validated emergency weight estimation tool, includes pre-calculated drug doses by colour zone. PAWPER XL tape: improved accuracy in obese children. Parental estimation: parents usually accurate within 10%. Habitus-modified Broselow (PAWPER): adjusts for body habitus. WHO weight-for-age tables: gold standard for nutritional assessment but requires charts.
What is the normal weight gain pattern in infancy?
Birth weight doubles by 4–5 months and triples by 12 months. Expected weight gain: 0–3 months: ~25–30 g/day; 3–6 months: ~15–20 g/day; 6–12 months: ~10–15 g/day. A neonate loses 5–10% of birth weight in first week (physiological) and regains it by day 10–14. Failure to regain birth weight by day 14 requires investigation (breastfeeding assessment, infection, metabolic).
What weight indicates moderate acute malnutrition in Indian children?
Using WHO/IAP standards: Weight-for-height Z-score <-2 to -3 = moderate acute malnutrition (MAM). Weight-for-height Z-score <-3 = severe acute malnutrition (SAM). In India, MUAC (mid-upper arm circumference) is also used: MUAC <11.5 cm = SAM in children 6–59 months; 11.5–12.5 cm = MAM. SAM with complications (oedema, medical complications) requires inpatient NRC (Nutrition Rehabilitation Centre) admission.
How is paediatric drug dosing different from adult dosing?
Children are not small adults — drug metabolism, distribution, and elimination differ significantly by age. Neonates have immature hepatic and renal function (lower clearance). Drug distribution differs (higher total body water in infants). Always calculate dose per kg and compare against maximum adult dose — never exceed it. Use paediatric formularies (IAP drug handbook, BNFc) rather than extrapolating adult doses. Double-check all paediatric calculations independently.
Key takeaway: Approximating weight metrics in high-acuity pediatric cases allows for rapid drug configuration alignment. To minimize dosing accidents, confirm calculations via length-based tools (like the Broselow tape) and crosscheck answers before injecting.
Medical disclaimer: This calculator is for educational and decision-support use only. Treatment choices rest explicitly with the evaluating physician.