A z-score measures how far a measurement is from the average in standard deviations. A z-score of 0 is average, +1 is one standard deviation above, and -1 is one below. Most healthy babies fall between -2 and +2.

Why use WHO standards?

WHO growth standards are based on healthy breastfed infants from diverse populations worldwide. They represent how children should grow under optimal conditions, making them the gold standard for birth to 24 months.

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Baby Growth Percentile Calculator

Track your baby's growth against WHO standards. Enter weight, length, or head circumference to see percentile rankings and z-scores from birth to 24 months.

Last updated: April 1, 2026

Sex

Units

Age

months

Weight

lbs

Length

Head Circ.

How to Use This Calculator

Select your baby's sex (boy or girl).
Choose the measurement type: Weight-for-Age, Length-for-Age, or Head Circumference.
Enter your baby's age in months (0-24).
Enter the measurement value in your preferred units.
Click Calculate to see the percentile ranking, z-score, and growth status.

The Formula

Percentile is calculated using the WHO LMS method: Z = ((Value/M)^L - 1) / (L × S), where L, M, S are age- and sex-specific parameters from WHO growth standards.

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Frequently Asked Questions

A percentile shows how your baby compares to others of the same age and sex. The 50th percentile is average. The 25th percentile means 25% of babies weigh less. Healthy babies can be anywhere from the 5th to 95th percentile.