Infant Monthly Growth Calculator (WHO Standards)
Track your baby's weight, length, and head circumference percentiles (0-12 months) using WHO growth standards. High-precision calculator for boys and girls.
About
Watching a baby grow is one of the most exciting parts of the first year, but deciphering growth charts can be confusing. This Infant Growth Calculator uses the WHO (World Health Organization) Child Growth Standards, which are the global benchmark for breastfed and formula-fed infants alike. Unlike older charts (like CDC 2000) that often normalized faster weight gain, WHO standards describe how children should grow under optimal conditions.
This tool calculates the precise percentile for weight-for-age, length-for-age, and head circumference-for-age. Percentiles are not grades. A baby in the 15th percentile is just as healthy as a baby in the 85th, provided they follow their own curve consistently. This calculator is designed to provide reassurance and clarity, helping you visualize your child's unique growth trajectory.
Formulas
We use the WHO LMS method to calculate Z-scores and Percentiles. The Z-score indicates how many standard deviations a measurement is from the median (average).
Where L (Box-Cox power), M (Median), and S (Coefficient of Variation) are specific constants for each age and gender from the WHO database.
Reference Data
| Age | Boys Median Weight (50%) | Girls Median Weight (50%) | Boys Median Length | Girls Median Length |
|---|---|---|---|---|
| Birth | 3.3 kg (7.3 lb) | 3.2 kg (7.1 lb) | 49.9 cm | 49.1 cm |
| 1 Month | 4.5 kg (9.9 lb) | 4.2 kg (9.2 lb) | 54.7 cm | 53.7 cm |
| 2 Months | 5.6 kg (12.3 lb) | 5.1 kg (11.2 lb) | 58.4 cm | 57.1 cm |
| 3 Months | 6.4 kg (14.1 lb) | 5.8 kg (12.8 lb) | 61.4 cm | 59.8 cm |
| 6 Months | 7.9 kg (17.4 lb) | 7.3 kg (16.1 lb) | 67.6 cm | 65.7 cm |
| 9 Months | 8.9 kg (19.6 lb) | 8.2 kg (18.1 lb) | 72.0 cm | 70.1 cm |
| 12 Months | 9.6 kg (21.2 lb) | 8.9 kg (19.6 lb) | 75.7 cm | 74.0 cm |