Free Pregnancy Tool
Child Height & Weight
Enter your baby's sex, birth date, measurement date, weight and length. We place them on the WHO growth charts from birth to 2 years.
General information only, not medical advice. Ask your doctor or midwife.
How this works
Formula: WHO LMS method: z = ((measurement ÷ M)^L − 1) ÷ (L × S); percentile = normal distribution of z.
- The World Health Organization growth standards give three numbers (L, M and S) for each month of age, for boys and girls.
- We work out your baby's exact age, blend the numbers for that age, and turn the measurement into a z-score.
- The z-score becomes a percentile. The 50th percentile is the middle; at the 25th, 25 of 100 babies the same age measure less.
- One reading matters less than the trend over time. Your doctor looks at the whole curve.
Everything is worked out in your browser. Belly Weekly does not send or store your answers.
Questions
Is a low percentile bad?
Not by itself. Healthy babies sit all across the chart. Your doctor watches whether your baby follows their own curve.
Why WHO charts?
The CDC recommends the WHO growth standards for children under 2 in the United States, and many countries use them.
Should I use corrected age for a premature baby?
Doctors often do. Ask your doctor which age to use on the chart.