Is this the same as my baby's centile?

No. It compares your baby to the WHO average only, as an approximation. The exact centile is plotted by your health visitor on the official WHO growth chart, usually in your baby's red book.

My baby is below average. Is that a problem?

Not on its own. Plenty of healthy babies sit below the average, and twins are often lighter. What health professionals watch is the pattern along a baby's own centile over time, not a single reading.

How often should babies be weighed?

Usually no more than monthly for the first six months, then less often, unless there is a specific concern. Frequent weighing tends to cause worry over normal fluctuations.

Baby weight percentile calculator (WHO average)

Baby weight-for-age checker

Sex

Age (months)

Weight

Unit

An approximation, worked out in your browser. Not a plotted centile.

What this shows, and what it does not

This compares your baby's weight to the WHO average for their age and sex. It is a quick sense-check, not the exact centile. The real centile is plotted by a professional using the full WHO chart, which accounts for the spread of healthy weights far better than a single average.

The trend is what matters

One weight is a snapshot. Health teams look at how a baby tracks along their own line over weeks and months. A baby steadily following their curve is usually thriving, whatever the number. If the trend shifts sharply, or you are worried, speak to your health visitor or GP.

Quick answer

This checker compares your baby's weight to the WHO average (the 50th centile) for their age and sex, so you can see roughly whether they are around, above or below average. It runs in your browser. It is an approximation, not a plotted centile: your health visitor plots the exact centile on the official WHO chart, and the trend over time matters far more than a single number.

How to use it

Choose sex and age. Pick boy or girl and enter your baby's age in months, from 0 to 24.
Enter the weight. Type the weight and choose kilograms or pounds.
Read the comparison. You get how your baby compares to the WHO average, with a reminder to use the official chart for the exact centile.

Frequently asked questions

Is this the same as my baby's centile?: No. It compares your baby to the WHO average only, as an approximation. The exact centile is plotted by your health visitor on the official WHO growth chart, usually in your baby's red book.
My baby is below average. Is that a problem?: Not on its own. Plenty of healthy babies sit below the average, and twins are often lighter. What health professionals watch is the pattern along a baby's own centile over time, not a single reading.
How often should babies be weighed?: Usually no more than monthly for the first six months, then less often, unless there is a specific concern. Frequent weighing tends to cause worry over normal fluctuations.