Baby clothes sizes: how to get the gift right

The number on the label isn't an age or a weight but the maximum body length the garment is made for. Size 62 fits a baby up to about 62 cm, and covers everything from roughly 57 cm. This comes from the European standard EN 13402, which labels children's clothing by body height. Plenty of clothes sold in New Zealand carry an age range or a size code instead, so check what the label actually says.

The age that shops print next to a size (say "2–4 months") is only a conversion based on an average child. According to the WHO growth standards, an average boy measures about 61 cm at three months and around 76 cm at one year, with girls a centimetre or two shorter. Any individual baby can easily be a whole size off the average, in either direction.

Two more practical points: a double size such as 62/68 means the piece will last across both sizes (it's usually roomier or has turn-up cuffs), and cotton shrinks a little after its first hot wash. Cuts also vary from brand to brand – with some makers a 68 comes up narrow and short.

An adorable little all-in-one in size 50 is the gift most likely to end up in a box with the tag still on. There are four reasons why.

Babies are born right on the edge of it. The average newborn is around 50 cm long, so half of all babies are bigger than size 50 from day one. And babies grow fastest in their first weeks – according to the WHO curves, they gain roughly 4 cm a month over the first two months.

Everyone gives it. A "new baby" gift tempts you towards the smallest size because it looks the cutest. Parents end up with ten pieces in size 50 and only a few weeks to wear them.

The first weeks are all about comfort. A newborn gets changed several times a day, so bodysuits, sleepsuits and zip-up onesies win every time. Little dresses with buttons down the back or a smart shirt practically never get a turn in the first six weeks.

The season doesn't match. A thick snowsuit in size 56 for a baby born in October won't get any use in winter, because by June the baby will be three sizes bigger.

Size 44 is made for premature babies, who are born smaller and lighter. You won't usually find it in ordinary shops, and it doesn't belong in the layette for a full-term baby – even a small newborn will probably fit it for only a few days.

If a baby has arrived early, though, it's exactly the gift the parents don't have: they weren't expecting the baby so soon and a standard size 50 is too big. Ask first what they need – hospitals often have rules about what premature babies can wear, and front fastenings and soft seams matter far more than looks.

A rough layette for a full-term baby for the first three months. The quantities are a sensible starting point, not a rule – it depends on how often you do the washing.

Clothing is the gift most likely to miss, because you're aiming at a number that changes every month. If in doubt, stick to the rule "two sizes up from what the baby wears now", or choose a gift that doesn't depend on size at all. You'll find ideas on how to share out new-baby gifts with others in Gifts for a new baby: three piles and what goes where.

If you'd like to give something the baby won't outgrow in a month, it could be a personalised book in which the child, drawn from a photo, is the hero. For a baby it's more of a gift for later – it comes into its own once they can listen to a story, for example for a first birthday.