What it is
The Growth Percentile Calculator compares a baby's weight and length to the WHO Child Growth Standards, returning a percentile (0–100) and a z-score (standard deviations from the median).
0–24 months Evidence-based Free & private
Baby Growth Percentile Calculator (WHO 0–24 months)
Plot your baby's weight and length against WHO Child Growth Standards. Get percentiles and z-scores instantly.
Category
Growth
Trust
Medical-grade
Weight-for-age
50th
z = 0.00 · WHO median 9.6 kg
Length-for-age
50th
z = 0.00 · WHO median 75.7 cm
Percentiles <3 or >97 warrant clinical follow-up. Percentile trend over time is more important than a single reading.
Medically reviewed by ASQCalculator Editorial Team
Understanding this tool
Plain-language explanations grounded in current pediatric evidence.
TL;DR
Plot your baby's weight and length against WHO Child Growth Standards (0–24 months). The calculator returns a percentile (where your baby falls among peers) and a z-score (how far from the WHO median). Trend along a curve matters more than a single number.
How it's calculated
For each measurement we compute z = (value − WHO median) ÷ WHO standard deviation for the child's age and sex, then convert to a percentile using the normal distribution. The full WHO standard uses an LMS power transform; this tool uses a normal approximation for ages 0–24 months.
When to use it
Use at every well-baby visit to verify growth is tracking along a consistent percentile curve.
Who should use it
Parents, pediatricians, nurses, lactation consultants, and dietitians.
Clinical importance
A single percentile is less informative than the trend. Crossing two major percentile lines (up or down) over a few months warrants discussion with your pediatrician.
Example
A 12-month-old boy weighing 9.6 kg and measuring 75.7 cm is at the 50th percentile for both weight and length — typical growth.
How to use this calculator
- 1Select sexBoy or girl — WHO percentiles are sex-specific.
- 2Enter age in months0–24 months. Use corrected age for preterm babies.
- 3Enter weight (kg) and length (cm)Use a calibrated scale and a measuring board for length.
- 4Interpret the resultRead the percentile and z-score. Compare with previous visits to see the trend.
Common mistakes to avoid
- Measuring length with the baby standing — under 2 years it must be recumbent (lying down).
- Using clothing or diaper weight without subtracting it from the total.
- Reacting to a single reading instead of looking at the trend across visits.
- Forgetting to apply corrected age for preterm babies.
- Comparing a WHO percentile with a CDC percentile — they use different reference populations under 24 months.
Glossary
- Percentile
- Position relative to peers — the 70th percentile means 70% of same-age, same-sex children are below this value.
- Z-score
- Standard deviations from the median; 0 is the median, ±2 are roughly the 2nd and 98th percentiles.
- WHO Child Growth Standards
- International growth standards based on optimally-fed, healthy children from six countries.
- Weight-for-age
- Weight compared to other children of the same age and sex.
- Length-for-age
- Recumbent length compared to peers; reflects long-term nutrition and health.
Medical references
Frequently asked questions
Answers parents and pediatric professionals ask most often about this tool.
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- Medically reviewedAligned with AAP & CDC
- Evidence-basedOfficial ASQ-3 cutoffs
- Mobile-firstBuilt for phones & tablets
Medical disclaimer. This calculator is an educational tool and does not replace evaluation by a qualified pediatric clinician. If you are concerned about your child's development or health, contact your pediatrician.