Diaper sizes go by weight, not by age

Read the pounds, ignore the months

Every diaper box prints a weight range, and that range is the whole of the sizing system. Age appears on some packaging as a courtesy and it is the least reliable thing on the box, because two babies of the same age can be a full size apart.

The ranges overlap deliberately. A baby at the top of one size and the bottom of the next will fit both, which is a feature: it means the changeover is a window rather than a cliff, and you can finish the box you have.

Count matters as much as size

A 22 count pack and a 210 count mega box of the same brand are not comparable purchases. The small pack is a top-up or a trial; the mega box is a month of your life committed to one size.

Buying a mega box in the size your baby currently wears is the classic overshoot. By the time you reach the bottom of it, the size below may no longer close. Buying the big box one size up and the small pack in the current size is the usual fix.

Gaps on this shelf

Worth knowing before you plan around this catalogue: the sizes listed here are newborn, 1, 3, 4, 6 and 7. Sizes 2 and 5 are not on the shelf at all. If you are stepping up gradually you will hit that gap and need to fill it elsewhere.

This is a listing gap rather than a manufacturing one. What resellers stock and what the brand makes are two different lists, and this page can only speak to the first.