How to choose a diaper size by weight

The size chart, the signs it's time to move up, and the mistakes parents make most often.

Diaper size is chosen by weight, not by age. Children of the same age can differ by two or three kilograms, so the number on the pack is a weight range, not a number of months.

Neighbouring sizes always overlap — 4–9 kg and 7–12 kg, for example. If your baby's weight falls in the overlap, go by build and by how the current diaper sits. A chunkier baby is more comfortable in the larger size, a slimmer one in the smaller.

Five signs it's time to move up: the diaper leaks around the edges at a normal load; the cuffs leave visible marks on the skin; the tabs fasten right at the very edge; the diaper sits low and slides down; the baby has passed the upper weight limit on the pack.

A common mistake is buying a size to grow into. A diaper that's too big doesn't sit against the legs, and leaks come from those gaps, not from a lack of absorbency. The other common mistake is waiting too long: a diaper that's too small presses on the tummy and fills up faster.