How much should a 4-month-old weigh?

On the WHO standards the average 4-month-old weighs about 7.0 kg (15 lb 7 oz) if a boy and 6.4 kg (14 lb 3 oz) if a girl. But "average" is just the 50th percentile — a healthy 4-month-old can weigh anywhere from roughly the 3rd to the 97th percentile. The full ranges for both sexes are in the tables above.

Should a baby double their birth weight by 4 months?

Many do, and doubling the birth weight is commonly reached between 4 and 6 months. It is a guideline, not a deadline: babies born larger or smaller, and those with their own growth pace, hit it a little earlier or later. A consistent curve is more reassuring than the exact week it doubles.

Is the 4-month weight the same for boys and girls?

No. Boys average a bit heavier than girls at every age, which is why the WHO publishes separate charts. At 4 months the 50th-percentile difference is roughly half a kilogram (about a pound). Always read your baby against the chart for their sex.

My 4-month-old is in a low weight percentile — should I worry?

Not on its own. The 3rd to 97th percentile is all within the normal reference range, so a baby at the 10th percentile who is feeding well, making plenty of wet diapers and following their own curve is usually thriving. What prompts a closer look is a curve that flattens or drops across visits — mention any sudden change to your pediatrician.

How much weight does a 4-month-old gain per week?

Roughly 140–200 g (about 5–7 oz) a week during the fast first-half-year growth, though it comes in bursts rather than evenly. A growth spurt around 3–4 months can mean a jump one week and a quieter week after. Weekly home weights bounce around; monthly trends are what count.

What is the average length and head circumference at 4 months?

Around 63.9 cm (25.2 in) length for boys and 62.1 cm (24.5 in) for girls at the 50th percentile, with average head circumference near 41.6 cm (16.4 in) for boys and 40.6 cm (16.0 in) for girls. The full percentile tables for length and head circumference are on this page alongside weight.

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WHO Growth Standards

Average Weight for a 4-Month-Old (WHO Percentiles)

The average weight of a 4-month-old boy and girl, the full percentile range from P3 to P97, and where your baby lands — using the WHO Child Growth Standards.

Is your 4-month-old's weight typical?

A quick weight-only check. For length, head circumference and exact age, use the full tool below.

Sex

Your baby's weight

Open the full growth percentile tool

Weight, length and head circumference at your baby's exact age in days.

Reference ranges from the WHO Child Growth Standards — not medical advice. Every baby grows differently.

Weight, length & head circumference percentiles at 4 months

The WHO reference values for a {{age}}-month-old, from the 3rd to the 97th percentile, for boys and girls. P50 is the average; anywhere from P3 to P97 is a normal, healthy measurement. Numbers are calculated directly from the WHO Child Growth Standards.

Weight-for-age

Sex	P3	P15	P50	P85	P97
Boys	5.6 kg12 lb 7 oz	6.2 kg13 lb 12 oz	7.0 kg15 lb 7 oz	7.9 kg17 lb 6 oz	8.6 kg19 lb 1 oz
Girls	5.1 kg11 lb 4 oz	5.7 kg12 lb 7 oz	6.4 kg14 lb 3 oz	7.3 kg16 lb 2 oz	8.1 kg17 lb 14 oz

Length-for-age

Sex	P3	P15	P50	P85	P97
Boys	60.0 cm23.6 in	61.7 cm24.3 in	63.9 cm25.2 in	66.1 cm26.0 in	67.8 cm26.7 in
Girls	58.0 cm22.8 in	59.9 cm23.6 in	62.1 cm24.5 in	64.3 cm25.3 in	66.2 cm26.1 in

Head circumference-for-age

Sex	P3	P15	P50	P85	P97
Boys	39.4 cm15.5 in	40.4 cm15.9 in	41.6 cm16.4 in	42.9 cm16.9 in	43.9 cm17.3 in
Girls	38.2 cm15.0 in	39.3 cm15.5 in	40.6 cm16.0 in	41.9 cm16.5 in	43.0 cm16.9 in

P50 (highlighted) is the median — the true "average". A baby is not "behind" at P15 or "ahead" at P85; both are well within the normal range. The trend along a baby's own curve over time matters far more than a single percentile.

Why 4-Month-Olds Gain Weight So Fast

The first six months are the fastest-growing stretch of your baby’s whole life. Most babies double their birth weight somewhere between 4 and 6 months, adding roughly 140–200 g (5–7 oz) a week through this period. If your 4-month-old suddenly looks rounder than the newborn you brought home, that is exactly what the WHO curves expect.

That speed is why a 4-month-old sits noticeably heavier on the chart than a newborn but the percentile itself usually holds steady. A baby who tracked around the 25th percentile at birth typically stays near the 25th now — the kilograms climb, the position on the curve does not. A percentile is just a comparison to other healthy babies of the same age and sex, not a grade.

This is also when many families notice growth looking a little less linear: a big growth spurt around 3–4 months can bring extra feeds and fussiness for a few days, then a plateau. One flat week is normal. What pediatricians watch is the shape of the curve across several visits, not a single weigh-in on a home scale.

Doubling the birth weight by 4–6 months is the classic milestone at this age. A steady curve — even a low or high one — matters more than hitting the 50th percentile.

Sources & Limitations

Every number on this page is computed from the World Health Organization Child Growth Standards (2006) — the international reference for how breastfed children grow under optimal conditions, used by pediatricians worldwide. These are population reference ranges, not targets to hit.

Reference ranges, not medical advice — every baby grows differently, and a healthy baby can sit anywhere from the 3rd to the 97th percentile. A low or high percentile is not a problem by itself; a curve that suddenly flattens, drops or jumps across visits is what's worth a conversation. For anything that worries you, talk to your pediatrician.

Watch the curve, not just today's number

Doudou plots your baby's weight, length and head circumference on the WHO growth curves as you log — so you see the trend that actually matters, not a one-off weigh-in. Synced between both parents.

Doudou — the baby tracker for both parents

Frequently Asked Questions

How much should a 4-month-old weigh?: On the WHO standards the average 4-month-old weighs about 7.0 kg (15 lb 7 oz) if a boy and 6.4 kg (14 lb 3 oz) if a girl. But "average" is just the 50th percentile — a healthy 4-month-old can weigh anywhere from roughly the 3rd to the 97th percentile. The full ranges for both sexes are in the tables above.
Should a baby double their birth weight by 4 months?: Many do, and doubling the birth weight is commonly reached between 4 and 6 months. It is a guideline, not a deadline: babies born larger or smaller, and those with their own growth pace, hit it a little earlier or later. A consistent curve is more reassuring than the exact week it doubles.
Is the 4-month weight the same for boys and girls?: No. Boys average a bit heavier than girls at every age, which is why the WHO publishes separate charts. At 4 months the 50th-percentile difference is roughly half a kilogram (about a pound). Always read your baby against the chart for their sex.
My 4-month-old is in a low weight percentile — should I worry?: Not on its own. The 3rd to 97th percentile is all within the normal reference range, so a baby at the 10th percentile who is feeding well, making plenty of wet diapers and following their own curve is usually thriving. What prompts a closer look is a curve that flattens or drops across visits — mention any sudden change to your pediatrician.
How much weight does a 4-month-old gain per week?: Roughly 140–200 g (about 5–7 oz) a week during the fast first-half-year growth, though it comes in bursts rather than evenly. A growth spurt around 3–4 months can mean a jump one week and a quieter week after. Weekly home weights bounce around; monthly trends are what count.
What is the average length and head circumference at 4 months?: Around 63.9 cm (25.2 in) length for boys and 62.1 cm (24.5 in) for girls at the 50th percentile, with average head circumference near 41.6 cm (16.4 in) for boys and 40.6 cm (16.0 in) for girls. The full percentile tables for length and head circumference are on this page alongside weight.