Baby clothes sizes: what should I buy?

woman shopping newborn baby clothes

by Emily Gilbert |
Published on

Choosing teeny baby clothes is one of the most fun parts of being pregnant and having a baby and although you'd think picking out the correct size for your little one would be straightforward, it can get a bit confusing.

Just like us adults, babies differ in shape and size and unfortunately not all clothing shops have consistently sized baby clothes meaning your child could end up being different sizes in different shops.

How do baby clothes sizes work?

Baby clothing sizes are based on a few different factors including age, weight and length and shops will go with the average size of a baby. But as most of us know, one baby will grow at a different speed than another, meaning for example that some 18-month-old babies might not fit into clothes specified for their age group.

How to work out your baby's clothes size

 • Before buying from a shop you've not bought from before, take a look at their sizing chart so you can double-check where your child's measurements fall before purchasing. Here are two examples from JoJo Maman Bebe and H&M...

Jojo Maman Bebe


 • A good rule to follow is that the clothing size on the label is usually the maximum size. So a romper that says it's for six months means babies up to six months old will be able to wear it.

 • You may find it easier to buy baby clothes in person as if your baby is already born, you'll probably have a good idea for knowing if an outfit will fit your little cherub.

• Naturally, the more baby clothes you buy from different brands, the easier it'll be for you to know which shops run big or small.

Baby clothes size by weight

As we say, sizes vary on brands so you should always check first but here's a general guide to give you an idea:

Weight: 10lb/4.5kg
Length: 56cm

0-3 months
Weight: 14.5 lb/6.5kg
Length: 62cm

3-6 months
Weight: 17.5lb/8kg
Length: 68cm

6-9 months
Weight: 20lb/9kg
Length: 74cm

9-12 months
Weight: 22lb/10kg
Length: 80cm
12-18 months**
Weight: 24lb/11kg
Length: 86cm

18-24 months
Weight: 26lb/13kg
Length: 92cm

What size baby grow should I buy for my newborn?

Surely newborn right? Unfortunately, it's not that simple. Most newborn clothes will fit babies up to ten pounds, which means that if you give birth to a bigger baby, it would be a tight fit. Similarly, even if the newborn size does fit your baby, it's worth remembering that it's unlikely a newborn baby grow would fit them for long, which is fine if you only want to use it a few times but not so much if you want to get more use out of it.

Instead, consider buying baby grows in sizes 0-3 months which should fit a baby up to 13/14 pounds.

You will probably already have an idea of what size baby you are due to have so this may help steer you in the right direction of what size baby clothes to buy.

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