Age at measurement
| Measurement | Value | Percentile |
|---|
Based on WHO Child Growth Standards for 0 to 24 months. One measurement on its own says little: doctors look at how your baby grows along a curve over time.
What does a percentile mean?
A percentile compares your baby with healthy babies of the same age and sex. If your baby is on the 40th percentile for weight, 40 out of 100 babies weigh less and 60 weigh more. The 50th percentile is the middle, but a baby on the 10th or 90th percentile can be just as healthy.
How this calculator works
It uses the WHO Child Growth Standards, which the CDC and the American Academy of Pediatrics recommend for all children under 2. These standards describe how breastfed babies grow in good conditions. For each measurement the calculator uses the WHO LMS values for your baby's exact age and sex to work out a z-score, then turns it into a percentile.
When should I talk to a doctor?
- A measurement is below the 3rd or above the 97th percentile
- Your baby crosses two or more major percentile lines (for example from the 50th to below the 15th)
- Your baby is not feeding well, has fewer wet nappies than usual, or seems unwell
Growth is judged over several measurements, so bring your baby's record to check-ups.
Premature babies
If your baby was born before 37 weeks, use their corrected age: their age from birth minus the number of weeks they were born early. Doctors usually do this until about 2 years old.
Frequently asked questions
Is a low percentile bad?
Not by itself. Some babies are naturally smaller. What matters most is that your baby keeps growing steadily along their own curve.
Why use WHO charts and not CDC charts?
For children under 2, the CDC recommends the WHO standards because they are based on healthy breastfed babies. CDC charts are used from age 2.
Can I use pounds and inches?
Yes. Choose lb and inches in the Units box and the calculator converts them.
How should length be measured?
Babies under 2 are measured lying down, from the top of the head to the heels, with legs straight. Home measurements are less accurate than clinic ones.
Is my information saved?
No. The calculation runs in your browser and nothing is stored.