Baby Clothes Sizes Explained

baby clothes hanging on a line

Where do we start with baby clothes? Your little one will grow so fast, particularly in the first year, that they may only wear clothes a few times before you need to discard them and buy some more in a larger size. There are different sizes to consider; preemie, newborn, 0-3 months, 3-6 months, 6-9 months, 9-12 months (6-12 months), 12-18 months and 18-24 months. When should your baby really switch between them?

You also need to think about how many clothes to buy. How many hats, socks and sleep suits do you really need? It’s easy to go over the top and buy too much, especially for newborn babies. This is a rookie mistake many experienced parents look back and regret. In this article, let’s look at baby clothes in more detail looking at the different sizes, how it can vary between different retailers (why can’t there be a uniform size everywhere?), how many clothes you should buy and how the clothes should fit on your baby. Ready? Let’s dig in…

How should you choose baby clothes?

Although you will undoubtedly want to choose clothes based on your baby’s age, this is sometimes not the best strategy. This is because all babies are different shapes and sizes. Some will be slimmer with a thinner waistline and longer legs, where as some will be a little shorter and bigger around the tummy. This can make choosing clothes very challenging, as a 5 month old baby may need 6-9 month clothing, or even bigger! Therefore, try to follow this advice:

Think of the size on the label as the main guide to finding the right clothes, NOT age.

You also need to factor in the different measurements between retailers.  Unfortunately there isn’t a uniform size for each size category. While there aren’t massive differences, you may find one particular brand is better than another and fits your baby a little better. If you find Walmart clothes fit nicely on your baby, you probably want to stick with this retailer for a while and buy other clothes there.

How do you read baby clothes sizes?

If there is a range of months on the label e.g. 0-3 months, you can take that to mean the clothing should fit an average baby up to 3 months. So you want to look at the second number and use that as your guide for the upper limit. Remember it doesn’t matter if there is a bit of growing room in the clothing when you first put it on your baby. Don’t worry if it looks a little baggy!

However, you may also find a label which just has 1 number e.g. 6 months. This generally means it’ll be suitable for babies aged between 3-6 months. Here’s a breakdown of this below:

  • 3 months = suitable from 0-3 months
  • 6 months = suitable from 3-6 months
  • 9 months = suitable from 6-9 months
  • 12 months = suitable from 9-12 months (in some cases it could mean 6-12 months – so check the weight and height limit carefully)
  • 18 months = suitable from 12-18 months
  • 24 months = suitable from 18-24 months

What are the sizes of baby clothes?

The main sizes you will find in stores are the following. Please note your local retailer may just have one number indicating the upper age limit.

  • Preemie
  • Newborn
  • 0-3 months
  • 3-6 months
  • 6-9 months
  • 9-12 months (some retailers stock 6-12 months instead)
  • 12-18 months
  • 18-24 months

Let’s look at these sizes in more detail.


If your child is born a little early, you still have some choice in terms of clothing, although not quite as much as the larger baby sizes. You may have more luck shopping online, because going in person might mean going to several retailers to find something you like. Preemie clothing is for babies who weigh around 5-6lbs with a length of up to 18 inches.


This is the first main size for full-term babies. It is for babies who weigh between 5-8lbs and who are up to 21.5 inches in length. However, it’s quite common for parents to go over the top and buy too many newborn clothes. You may only be able to use newborn clothes for a couple of weeks if your baby has an above average birth weight. In many cases, you’ll be better off buying a few more 0-3 month size clothes than newborn ones. If the clothes look a little big on your newborn, it’s no big deal.

Click here for a comparison between preemie and newborn clothing

0-3 months

After newborn size clothing comes 0-3 months. On average you should find this size is for babies who weigh 8-12lbs and who are between 21.5-24” in length. Like other sizes though, there will be some subtle differences in measurements between various brands. In general, you should think of this size as meaning ‘up to 3 months’.Your baby might be fine in 0-3 month clothing until they are 4 or 5 months old, but on the other hand they may need it a week after their birth, or from day 1.

Visit here for some more info on the 0-3 month size

3-6 months

Depending on the size of your baby, they may be ready to wear 3-6 month clothing when they are only a couple of months old, or they may still be fine wearing it when they are 8 months old. You should find this clothing size is for babies who weigh around 12-18lbs and who are 24-27” in length, although there might be some slight differences in some stores.

Click here for a detailed look comparing 3-6 month and 0-3 month sizes

6-9 months

Like other baby clothing sizes, you need to look at the second number to work out what clothes your baby should be wearing (although sometimes you may just see a ‘9 month’ label). 6-9 months means for most infants, this size should be fine up to the age of 9 months. In terms of weight and length, 6-9 month clothing is suitable for babies who are between 17-20lbs and 26-28 inches long

Here’s an article comparing the 3-6 and 6-9 month sizes

9-12 months and 6-12 months

9-12 months is the final size in your baby’s first year (and I guarantee you’ll reach this point before you can blink!). This size is for babies who weight between 20-24lbs and who are 28-30 inches tall.

However, you may also find some retailers stock 6-12 months instead, which may save you a bit of money as you use these clothes for a bit longer. There’s no rule about this and it just depends on how each brand wants to arrange their clothing sizes. However, both sizes are suitable up to the age of 12 months.  On average, 6-12 months is suitable for babies who weigh between 17-24lbs and who are 26-30 inches in length.

Here’s an article looking at the differences between 6-12 and 9-12 months.

12-18 months

Once you get past the first year, you start to see bigger age ranges in clothing sizes as your baby starts to grow at a slightly slower rate. For 12-18 month clothing (you may just see 18 months on the label), this is for toddlers who are between 24-28lbs and 30-32 inches in height.

18-24 months

This is the last size in baby clothing, although you may already want to consider the toddler clothing range at this point, especially if your toddler is moving around freely and hardly crawls any more. In fact, you may even want to look at toddler clothes before this, just after they turn 12 months old if they are already fairly mobile. 18-24 (or just 24 month) clothing is for toddlers who weigh between 28-30lbs and have a height of between 32-34 inches.

Click here for more info on 12, 18 and 24 month baby clothing

How do you know what to buy?

Obviously you can’t really try clothes on your baby in the store, so what should you do? Firstly, you need to ensure you know your baby’s weight and length before you go shopping. You don’t need to do this every time, but just be aware of it every so often. Then when you check a clothes label in the store, you’ll have a better idea what will fit your baby. Remember if in doubt buy something slightly bigger. Babies don’t mind if their clothes are a little baggy!

Chart – US baby clothing sizes compared UK and European sizes    

Here is a chart showing how baby sizes compare between the UK, USA and Europe. The UK and USA are almost the same, but in Europe they measure everything in centimetres rather than using an age range on the label.

Baby clothes size chart by brand

Here is a breakdown of all the different height and weight ranges of various brands in US stores for baby clothing sizes. You can see there are a few differences between them. Nordstrom seem to cater for larger babies, where as Walmart look a good bet for smaller infants.





How many baby clothes do you need?

It’s easy to go over the top and buy too many clothes for your baby. You can see from the charts above how quickly they grow so you probably won’t get that much use out of a set of clothing, before moving up a size. Remember, if in doubt, buy something which is slightly larger than smaller. Your baby won’t mind, and it’ll give them some wiggle room.

How often will you do the laundry?

In terms of how many items you need, it depends how often you intend to do laundry. If you and your partner are working full-time and you don’t have much time to household chores, you might be wise to have enough clothing to last your baby a whole week, or a few days before putting everything in the washing machine. However, if you like to do laundry three or four times a week, you can get away with buying less clothing.

Assuming you do your laundry a couple of times a week, here is a rough guide on what clothes your baby needs:

  • 4 sleepsuits
  • 4 pairs of leggings
  • 3 jumpers
  • 3 tops
  • 8 bodysuits
  • 3 rompers
  • A coat
  • 5 pairs of socks
  • 2 hats
  • 2 pairs of mittens

How do you know if baby clothes are too small?

Usually it’s pretty obvious if your baby’s clothes are too small, as it can be difficult to put them on. That being said, here are some other telltale signs:

  • You see clear space between their shirt and their pants.
  • It’s really difficult to attach the poppers between their legs on a bodysuit or sleepsuit.
  • You see a red line on their skin where the elastic from some clothing has irritated their skin.
  • The sleeves don’t roll up comfortably and appear tight on the arms.

Should you buy baby clothes which are too big?

It’s obviously better if your baby’s clothes are slightly too big than too small, as they’ll feel more comfortable wearing them. It also means they can use the clothes for longer, saving you a bit of money in the process. However, the clothes shouldn’t be too big, especially sleepwear, as it can present a suffocation risk. The clothing may get tangled up when they’re sleeping and cause breathing issues. Just use your judgement when you choose baby clothes. If they look really baggy on your baby, then they’re probably too big. For example, maybe their feet don’t reach the bottom of their onesie properly, or if your baby is walking and tripping over too much it might be because of the clothing.

When to move up a size in baby clothes?

Ideally you want to be ahead of the game when you’re choosing clothes for your baby. If you wait until you see visible signs that the clothes are too small, such as red marks on their skin, difficulty rolling up sleeves etc, it means you should have upsized sooner. If in doubt, or if you don’t know your baby’s exact size, always size up. For example, if your baby is 3 months old, choose 3-6 month clothing (not 0-3 months).

When should you move to toddler size clothing?

Although baby clothing sizes start from newborn (or preemie) until 24 months, your little one can definitely switch to toddler clothing beforehand. Toddler clothing will have a different style to baby clothes, so it’s more suitable for small children e.g. no poppers anymore! Pants have thinner waists with longer leggings and tops will have longer sleeves, to accommodate children who are very mobile and comfortable walking. You may consider toddler clothing from 12-18 months onwards if your baby is an early bloomer in terms of walking, and if they are big for their age.

baby clothes sizes explained