Baby Weight Calculator: Is Your Baby Growing Well?
Every parent wonders whether their baby's weight is on track. This calculator compares your baby's current weight to WHO average growth standards for their age and sex — giving you a quick snapshot of where they fall on the growth spectrum.
WHO Growth Standard Averages (Boys)
| Age (months) | Average Weight (Boys) | Average Weight (Girls) |
|---|
| Birth | 3.3 kg | 3.2 kg |
| 2 months | 5.6 kg | 5.1 kg |
| 4 months | 6.7 kg | 6.2 kg |
| 6 months | 7.9 kg | 7.3 kg |
| 9 months | 9.2 kg | 8.6 kg |
| 12 months | 10.2 kg | 9.5 kg |
| 18 months | 11.5 kg | 10.8 kg |
| 24 months | 12.7 kg | 12.0 kg |
Check your baby's weight against these averages with our Baby Weight Calculator.
What the Weight Comparison Means
- Being above or below the average is not automatically cause for concern.
- The trend — whether the baby is growing consistently along their curve — matters more than any single measurement.
- Premature babies should be assessed using their corrected age (subtract weeks of prematurity from actual age).
- Exclusively breastfed babies may grow differently in the first months compared to formula-fed babies.
Growth Patterns to Monitor
- Normal: Consistent growth along a percentile line — even if that line is the 10th or 90th percentile.
- Concern: Dropping two or more percentile lines between health visits.
- Alert: Weight loss after initial newborn loss (most babies lose 5–10% in the first week, regaining by day 10–14).
Practical Tips
Use the Red Book / health record at every visit. Your baby's growth chart is plotted at every check-up — this visual record is the most reliable growth monitor available.
Weigh at the same time and conditions. Before a feed, without clothes, on the same scale for meaningful comparisons.
Ask your health visitor or paediatrician about specific percentiles. This calculator provides an average comparison — your healthcare provider can plot your baby on official WHO percentile charts.
Final Thoughts
Baby weight tracking gives parents reassurance and helps health professionals identify early signs of growth concerns. The trend over time is what matters most.
Compare your baby's weight with our free Baby Weight Calculator.
Consult your paediatrician or health visitor for accurate percentile plotting and clinical assessment.