Baby Length Percentile Calculator

Enter the measured length, age-group average, and standard deviation to find the percentile.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

Growth charts express how a baby’s measurement compares to peers of the same age using the normal distribution: a z-score — how many standard deviations a measured length is from the age-group mean — is converted into a percentile that says what share of babies that age are shorter. This is the same statistical logic behind the WHO and CDC growth charts pediatricians use.

This calculator computes the z-score and percentile from a baby’s measured length, the age-group’s average length, and its standard deviation. It’s an informational tool for parents curious how a measurement compares to typical growth patterns, and it mirrors the calculation pediatricians perform when plotting a growth chart — though it isn’t a diagnostic tool and doesn’t replace a clinician’s assessment of an individual child’s growth.

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