How baby clothes sizing works.

Do you know how baby clothes sizing works? When you see a great baby clothes deal,can you buy ahead with confidence or is it really just a crap shoot?

Guessing what size your baby will be in the future can be a frustrating experience. It’s all very well for brands to label a piece 3-6 months… but there’s no guarantee that your baby will fit into it for the whole of that time frame. 

What gives?

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Are Baby Clothes Sizes Accurate?

Because we don’t have enough on our plates as new moms, baby clothes sizes can vary dramatically between brands. There’s no standard to sizing.

However, you’re usually pretty safe if you’re sticking with a particular brand and style. So, if you’re buying packs of Carter’s onesies, you’ll find the Newborn, 0-3, 3-6 (and on) follow the progression in sizes pretty well. But, if you suddenly start buying a different brand you might find the sizes very different.

Frustrating? Yes.

What Are the Basic Baby Clothes Sizes?

Most baby clothes sizes are labelled as follows:

  • Preemie – weight up to 6 pounds
  • Newborn – up to 7 pounds and 19 inches
  • 0-3 months – 7-12 pounds. Length: 19-23 inches 
  • 3-6 months – 12-16 pounds. Length: 23-25 inches 
  • 6-9 months – 16-20 pounds. Length: 25-27 inches 
  • 6-12 months – 17-22 pounds. Length: 27-29 inches
  • 12-18 months – 22-27 pounds. Length: 29-32 inches

What if There’s No Size ‘Range’ On the Item?

Some brands don’t put a size range on their clothes: it’ll just say (for example) 3 months. It might include a weight and a length too, but it might not.

What does this mean?

Does this mean 0-3 months or 3-6 months?

In my experience it means ‘up to’ though the clothing item might be slightly on the larger size.

So, if it says 3 months on the tag, it’ll fit like a (slightly larger) 0-3 month outfit.

How Fast Do Babies Outgrow Their Clothes

Ok, I’m a bit nerdy. Are you? (We should be friends!)

Do you remember being given a growth chart by your paediatrician or at the hospital?

(If not, I’ve got some links for you in a second.)

The idea is you should be able to plot your baby’s growth against their percentile line over time. 

If you do that from birth, you should have some idea when your baby will reach those weight milestones and might be ready to move up sizes.

It’s not an exact science (lots of mights and shoulds in there…), but for those Type-A people among us it’s a bit of a guide.

Here are the growth charts from the CDC from birth to 24 months:


Can I Skip Newborn Size Baby Clothes?


I know, not the definitive answer you want to hear (again… it’s a bit of a crapshoot) 

The thing is, some babies will be big enough to skip newborn and go straight into 0-3 month size. And some won’t.

Can you tell that from a late pregnancy growth scan? Not really – there’s so much room for error and there are endless stories of women being induced because they’re expecting a ‘massive baby’ only to have the poor mite come out quite normal sized…

There are some cases where you’ll almost definitely need newborn sizes (or even smaller):

  • If you’re expecting a premmie,
  • twins on board,
  • are being induced earlier than your due date,
  • if you’re measuring small for dates and/or you’ve had an ultrasound that confirms baby is on the smaller side.

You may be able to plan to skip straight to 0-3 month size if:

  • you make large babies (you’ve had one or more before.)
  • you and your partner are large people (mostly I mean tall, but big-boned counts too.) 
  • you’re measuring large for dates and/or you’ve had an ultrasound that suggests baby is on the big side.
  • you have gestational diabetes and baby is measuring large.

How Many Baby Clothes Do I Need in Each Size?

To be honest, I kitted out a basic wardrobe in every size for my little ones. Otherwise, you’re going to be under the pump to keep on top of the washing. And I don’t want to run out of baby clothes or have to stress about laundry.

But, you don’t have to do it expensively! 

With my first we used mainly hand-me-downs from a friend.

I bought a couple of new outfits at each size, including one or more ‘dressy’ outfit for family gatherings. 

What baby clothes do I need? <— this post has some basic guidelines of how many clothes you need for your baby’s wardrobe.

You may find you receive loads of 0-3 month baby clothes at your baby shower – they’re so cute! But, you probably don’t need that many as babies outgrow that size fast. Leave the tags on some of them and take them back to exchange for larger sizes.

It’s also best not to buy seasonal clothing too far in advance – basic onesies, go for it! But, winter coats and sleepers are best purchased close to the season when you have a better idea of what size baby will be (plus they’re some of the more expensive items so you don’t want to stock up and find they’re unwearable.)  

What if My Baby is Tall?

Babies come in all shapes and sizes. Including long and skinny!

It happens sometimes that baby exceeds the length of a clothing size before reaching the weight.

I never had that problem (we’re all shorties over here!)

The problem with outgrowing the length first is that the next size will likely be much wider in the shoulders… and not fit so great that way.

That’s fine with onesies (you can grab these awesome onesie extenders on Amazon to fix that problem), but is a little harder to deal with with sleepers and winter clothes. 

How to Tell When It’s Time to Go Up a Baby Clothes Size

Just because your baby reaches an age, height or weight milestone doesn’t mean they’re ready for the next size up. 

Watch your baby to determine when its time to go up a size.

One minute that cute little newborn sleeper will be swimming on them, the next minute they’ll be stretching the length. I like to move up sizes once the crotch-to-neck length is a little snug. If the neckline is being pulled downwards, it’s past time for the next size.

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