GROWTH GUIDE · BIRTH TO 24 MONTHS

Baby length percentile calculator

For babies under two, the relevant measurement is recumbent length: measured lying down, rather than standing height. The calculator uses the WHO length-for-age reference.

Calculate length percentile ↗

Take a consistent measurement

A length board and two trained people help make this measurement repeatable. Record the head-to-heel length while the baby is lying down. If you have only standing height, ask your clinician for an appropriate length measurement.

Understand the number

The 50th percentile is the middle of the reference distribution. A baby near the 25th percentile has a larger measurement than approximately 25% of the reference group at that age and sex. A percentile is not a percentage of ideal growth.

Small measurement differences can shift a percentile. Do not compare a standing height directly with the lying-down length reference used here.

Reference values by age

Newborn length reference 1 month length reference 2 month length reference 3 month length reference 4 month length reference 6 month length reference 8 month length reference 9 month length reference 12 month length reference 15 month length reference 18 month length reference 24 month length reference

Reference, not diagnosis

Talk to your healthcare professional about a measurement or trend that concerns you. This tool does not correct age for babies born prematurely.

Source: WHO length-for-age tables. Read the calculation methodology.

Review status: Maintained by Baby Growth and technically reviewed on 29 September 2026. Calculations and product ranges are checked against the cited WHO, CDC and manufacturer sources. This independent tool has not received clinical review and does not replace professional care.