Average Length for a 4-Month-Old Boy

The average (50th-percentile) length for a 4-month-old boy is 63.9 cm (25.2 in), based on the WHO Child Growth Standards. Across the healthy range, most boys this age measures between 60.0 cm (23.6 in) and 67.8 cm (26.7 in). (length is measured lying down until age 2)

What's typical at this age

Length gain slows a little to around 2 cm a month. By around 4–6 months many babies have added a quarter to their birth length. Between month 4 and month 5, the median boy grows about 2.0 cm.

A percentile compares your boy to other boys the same age — the 50th is simply the middle. Being above or below it is usually completely normal; a baby who has always tracked the 15th or 85th percentile is typically growing exactly as they should. What pediatricians watch for is a sudden change in the pattern, not the number itself.

Percentiles calculated from the WHO Child Growth Standards (2006). For information only — not medical advice. If you're concerned about your child's growth, speak to your pediatrician or health visitor. Full disclaimer.