Average Baby Height by Month (0–12 Months): WHO Reference Table

Height is the measurement parents obsess over least — until the pediatrician mentions their baby is 'short' or 'tall.' Then it becomes the only thing on your mind. Like weight, length falls into a normal range that spans from the 3rd to 97th percentile, and a baby at the 5th percentile is not short — they're small, which may simply reflect their genetics.

Here's the WHO data, explained in plain terms.

WHO Average Baby Length by Month: Boys

Length is measured lying flat until age 2, then standing height is used. These two measurements can differ by 0.5–1 cm, so you may notice a small jump or drop at the transition — that's normal.

Source: WHO Child Growth Standards — Length-for-age, boys

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WHO Average Baby Length by Month: Girls

Girls are typically 0.5–1.5 cm shorter than boys in the first year but follow the same growth velocity pattern.

Source: WHO Child Growth Standards — Length-for-age, girls

How Fast Do Babies Grow Each Month?

Length gain follows the same decelerating pattern as weight — fastest early, gradually slowing over the first year.

By 12 months, most babies have grown 25–30 cm from their birth length — roughly doubling their starting measurement.

The Measurement Problem with Infant Length

Unlike weight (which is objective once you have a scale), length measurement in infants has a human error factor. Getting an accurate length requires:

1. The baby lying flat on a firm surface
2. Head touching the top panel
3. Legs fully extended (which babies resist)
4. Feet flat against the bottom panel

In practice, small babies squirm. A result that's 1–2 cm shorter than last month is almost always technique variation, not a growth problem. If the number seems wrong to you, ask the nurse to re-measure.

When to Discuss Length With Your Doctor

Length on its own rarely triggers concern — but patterns do:

• Height consistently below the 3rd percentile when both parents are average or above average height
• Length dropping across two major percentile lines on the WHO chart (e.g., 75th → 25th over 6 months) — see why babies drop on the growth chart for likely causes
• Height slowing while weight continues to increase (can indicate certain hormonal conditions)
• Any complete halt in length gain for 3+ months after the first 2 weeks of life

For most healthy babies, the first conversation about height as a potential medical concern doesn't happen until age 2–3, if at all. For complete WHO length-for-age percentile tables, see the baby length-for-age chart reference.