1Paediatric Weight Estimation Formulas
During acute pediatric arrest, status epilepticus, or septic shock, obtaining a scale weight is frequently impossible. Standard estimation rules allow immediate initiation of time-critical interventions:
• APLS (1–5 years): Weight (kg) = 2 × (Age in years + 4)
• APLS (6–12 years): Weight (kg) = 3 × Age in years
• Luscombe-Owens (1–10 years): Weight (kg) = (3 × Age in years) + 7
• Nelson (<12 months): Weight (kg) = (Age in months + 9) ÷ 2
• Nelson (1–6 years): Weight (kg) = (Age in years × 2) + 8
• Broselow Tape: Length-based categorization from 46 cm to 145 cm (3 to 36 kg)
APLS vs. Luscombe-Owens: The classic APLS formula was developed in the 1980s and is easy to compute mentally. However, multiple contemporary validation studies in the UK, India, and Australia demonstrate that APLS systematically underestimates weight by 10%–20% in modern populations. The Luscombe-Owens formula (Weight = 3 × Age + 7) corrects for this bias and is preferred for children older than 1 year.
2Normal Paediatric Weight Reference Chart
| Age Milestone | WHO 50th Centile Median | APLS Estimate | Luscombe-Owens Estimate |
|---|---|---|---|
| Newborn | 3.5 kg | — | — |
| 3 Months | 6.0 kg | 6.0 kg | — |
| 6 Months | 7.5 kg | 7.5 kg | — |
| 12 Months (1 yr) | 10.0 kg | 10.0 kg | 10.0 kg |
| 2 Years | 12.0 kg | 12.0 kg | 13.0 kg |
| 5 Years | 18.0 kg | 18.0 kg | 22.0 kg |
| 8 Years | 25.0 kg | 24.0 kg | 31.0 kg |
| 10 Years | 32.0 kg | 30.0 kg | 37.0 kg |
| 12 Years | 40.0 kg | 36.0 kg | 43.0 kg |
3Key Resuscitation Dosing Principles
- Never exceed adult maximums: Paediatric doses must be capped at standard adult doses (e.g., maximum IV adrenaline in cardiac arrest is 1.0 mg; maximum IV amiodarone is 300 mg).
- Adrenaline (Epinephrine) Concentrations:
- Cardiac Arrest: 0.1 mL/kg of 1:10,000 solution (0.01 mg/kg) via IV or IO route.
- Anaphylaxis: 0.01 mL/kg of 1:1,000 solution (0.01 mg/kg) via Intramuscular (IM) route into anterolateral thigh.
- Defibrillation Energy: Initial and subsequent synchronized or unsynchronized shocks are delivered at 4 Joules/kg (AHA/ILCOR 2020 pediatric guidelines).
- Fluid Challenges: 10 to 20 mL/kg of balanced isotonic crystalloid (Ringer's Lactate or Normal Saline) administered over 5 to 10 minutes, with immediate reassessment for rales or hepatomegaly.
4Frequently Asked Questions
What is the APLS formula for pediatric weight estimation?+
For children 1–5 years: Weight (kg) = 2 × (Age in years + 4). For children 6–12 years: Weight (kg) = 3 × Age in years. For infants 1–12 months: Weight (kg) = (Age in months + 9) / 2.
What is the normal weight gain velocity in healthy infants?+
Birth weight typically doubles by 4–5 months and triples by 12 months. Expected weight gain rates: 0–3 months: ~25–30 g/day; 3–6 months: ~15–20 g/day; 6–12 months: ~10–15 g/day. Newborns normally lose 5%–10% of birth weight in the first week, which should be regained by day 10–14.
How should weight be estimated for obese children in an emergency?+
For resuscitation defibrillation energy, IM adrenaline, and blood volume challenges, use estimated actual weight. For hydrophilic maintenance infusions and drug dosing, calculate ideal body weight (IBW) to prevent accidental overdose. Length-based tools with body habitus adjustments (such as the PAWPER XL tape) provide the highest accuracy in obese children.
Clinical Takeaway: Mathematical weight estimation is an emergency surrogate when weighing is unfeasible. Whenever clinical stability permits, obtain a true scale weight and re-verify all infusion calculations.
Medical Disclaimer: This calculator provides decision-support estimates for emergency situations. Medication selection, routes, and doses remain the direct responsibility of the treating healthcare practitioner.