Paediatric weight estimate by age (APLS)
Estimate a child’s weight when you cannot weigh them.
What this calculator is for
In a paediatric emergency you need a weight for drug doses, fluid boluses and equipment sizes before you can put the child on a scale. These APLS formulas give a quick estimate from age. Replace it with a measured weight as soon as possible.
The formulas (APLS)
- Under 12 months: (0.5 × age in months) + 4 kg.
- 1–5 years: (2 × age in years) + 8 kg, which is the same as (age + 4) × 2.
- 6–12 years: (3 × age in years) + 7 kg.
Over 12 years, weigh the child; many adolescents are close to adult size.
Worked examples
- A 6-month-old: (0.5 × 6) + 4 = 7 kg.
- A 4-year-old: (2 × 4) + 8 = 16 kg.
- An 8-year-old: (3 × 8) + 7 = 31 kg.
Interpreting the estimate
The estimate is an average for well-nourished children. Use it to draw up first emergency doses, then recalculate maintenance fluids and regular medicines once the child is weighed. Write in the notes that the weight was estimated.
Limitations and pitfalls in Pakistan
- Stunting and wasting are common, so many Pakistani children weigh less than the formula predicts. An overestimate leads to overdosing, especially with fluids, paracetamol and sedatives.
- Children with severe acute malnutrition need a measured weight and the WHO malnutrition protocol; formulas are unsafe for them.
- Overweight children may weigh more than the estimate. For some drugs, dosing by ideal weight is safer; ask a senior or pharmacist.
- A length-based tape, where available, is usually more accurate than an age formula.
- Parents often know a recent weight from a clinic card or vaccination record. Ask before you estimate.
See paeds emergency, sepsis in children, the febrile child, the paracetamol and ibuprofen dose calculator, the maintenance fluid calculator and the textbook chapter on nutrition and malnutrition.
Frequently asked questions
What is the APLS weight formula?
Under 1 year: (0.5 × age in months) + 4. Age 1–5: (2 × age) + 8. Age 6–12: (3 × age) + 7. The answer is in kg.
How much does a 2-year-old weigh on average?
The APLS estimate is (2 × 2) + 8 = 12 kg, but many children are lighter, so weigh the child if you can.
Can I use the estimated weight for maintenance fluids?
Only until you can weigh the child. Maintenance fluids and regular drug doses should be based on a measured weight.
Is the APLS formula accurate for malnourished children?
No. It overestimates weight in undernourished children, which can lead to overdosing. Always weigh children with suspected malnutrition.
A calculator supports, but does not replace, clinical judgement. Check results before acting on them.