Baby clothes sizes explained: what fits when

The size bands you'll see

Most UK shops use age bands. The exact names vary, but you will usually find:

• Premature and tiny baby
• Newborn, sometimes also "up to 1 month"
• 0 to 3 months
• 3 to 6 months
• 6 to 9 months
• 9 to 12 months
• 12 to 18 months, then 18 to 24 months

Why the age on the label can mislead

Babies grow at very different rates, so a 4-month-old might fit 3 to 6 months, 6 to 9 months, or still be in 0 to 3. Brands also cut their clothes differently: a 3 to 6 month sleepsuit from one shop can fit like a 0 to 3 from another. Many parents end up with clothes in the "right" age band that simply don't fit.

What to check on the label

Most labels also give a weight and a height (or length) range. These are far more useful than the age. If your baby's weight or length is near the top of a range, they are likely to be moving up soon. Baby sleeping bags are usually sized by weight too, so check the manufacturer's guide rather than going by age.

Signs something is too small

• Poppers strain or pop open, especially at the crotch.
• Toes press against the end of a footed sleepsuit, or your baby curls their feet.
• Cuffs, waistbands or elastic leave red marks.
• It's a struggle to get it over their head.
• The body rides up or the legs end above the ankle.

Buying ahead without overbuying

• Don't stockpile the next size. You can't know when your baby will need it, or what season it will be.
• Think about seasons. A 6 to 9 month snowsuit is no use if your baby reaches that size in July.
• Gifts often come in bigger sizes. Keep a note of what you already have in each size before buying more.

Questions parents ask

Should I buy newborn or 0 to 3 months?

Many babies outgrow newborn sizes within a few weeks, so a small number of newborn items and more in 0 to 3 months usually works well. If your baby is expected to be particularly small or large, your midwife can give you a better idea.

Why does the same size fit differently from different shops?

There is no single UK standard for baby sizes, so each brand sets its own. Use the weight and height on the label and get to know which brands run small or large for your baby.

When should I move my baby up a size?

When you see the signs above, such as straining poppers or toes pressing against the end of a sleepsuit. It's usually time before the clothes look obviously small.