Baby Romper Size Guide

A romper, also called a playsuit, is a one-piece outfit that’s typically loose-fitting and made of cotton or a cotton blend. It’s perfect for summer weather because it’s lightweight and airy (skip straight to the Baby Romper Size).

Rompers come in a variety of styles, including short-sleeve, long-sleeve, and sleeveless. They also come in a variety of colors and prints, so you’re sure to find one that your baby will love.

Baby Romper Size Guide
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When it comes to baby romper sizing, some parents might be thinking: “Who cares? I’ll just take my baby to the store and buy whatever size is in stock.” But believe it or not, if you want your baby to look stylish and feel comfortable, you need to take the time to find the right size.

That’s why we’ve put together this comprehensive guide to baby romper sizes. We’ll show you the different sizing charts for different brands, so you can find the best fit for your child.

Jump right into the Frequently Asked Questions

Related: Romper Size Chart and Fitting Guide for Adults, Youth shoe size chart – US – UK – EU sizing, Foot Size Charts for Adults and Kids: What’s my shoe size?

Baby Romper Size Table of Contents

Baby romper size chart (standard)

Related: H&M Baby & Kids Sizes

Measure 3 mo6 mo12 mo18 mo24 mo
Center Back
Back Waist
Cross Back
(Shoulder to shoulder)
Arm Length
to Underarm
Upper arm(in.)67
Armhole depth(in.)4

Baby romper size chart by age

Related: Boys Growth Chart – A Useful Size Guide For boys Shoes And Clothing, US Size Guide Kids Clothes Size Chart

SizeChest Waist Height Trunk Length 
New born15.538.75164020.551.2521.152.75

How do you size a romper?

Related: Girls Growth Size chart – A Useful Guide For Shoes And Clothing

When it comes to sizing a romper, there’s a bit more to it than just the age of your child. You’ll need to take into account their weight and height as well.

Here’s a general guide to help you out:

  • Newborn: up to 7 pounds (≈ 3 kg), up to 21 inches long (≈53 cm)
  • 3-6 months: 7-12 pounds (≈3-5 kg), 21-24 inches long (≈53-61 cm)
  • 6-9 months: 12-16 pounds (≈5-7 kg), 24-26 inches long (≈61-66 cm)
  • 9-12 months: 16-20 pounds (≈7-9kg), 26-28 inches long (≈66-71 cm)

Learn more about how to measure for baby rompers (video)

Toddler clothing size chart by Suryashree Gullipalli

Frequently Asked Questions

When to size up or size down?

One of the most important things to keep in mind when shopping for baby rompers is to size up or size down, depending on the fit you’re looking for. For example, if you want a romper that’s a bit more snug, size down. But if you’re looking for a bit of extra breathing room, size up.

Pay close attention to the fabric weight and thickness, too. A thicker fabric will give your baby a more relaxed fit, while a thinner fabric will be snugger.

So when do you size up or size down? It really depends on the individual romper and your own preferences. Just use these guidelines as a starting point, and remember to always get the baby to try on the romper before buying it!

Should I size up in a romper?

Depending on the brand, a romper may run a little small. So if you’re in between sizes, it’s always a good idea to go for the larger size.

But there are also some brands that size their rompers a little large, so you may not need to size up at all. To be on the safe side, it’s always best to check the sizing chart on the brand’s website before you make your purchase.

Equally, use the baby romper size charts we have here to give you a good idea of what would be the best fit for your baby.

Should rompers be tight?

When it comes to buying baby rompers, should you go for a tight or loose fit? Well, that depends on your baby’s body type.

If your baby is on the thinner side, you may want to go for a tighter fit so the romper doesn’t fall off. But if your baby is on the chunkier side, you’ll want to go for a looser fit so the romper doesn’t squeeze them too tightly.

Of course, there are no hard and fast rules here. It’s ultimately up to you what you think looks best on your baby. Just keep in mind that a loose-fitting romper might not look as put together as a tighter-fitting one.

Are there plus-size rompers?

Yes, there are plus-size rompers! In fact, many retailers carry plus-size baby clothes these days. So no matter what your body type, you’re sure to find a romper that fits your baby perfectly.

Just be sure to measure your child before you buy. You don’t want to end up with a romper that’s too small or too big for them. That’s just frustrating for your baby.

When can I put my baby in a romper?

You can put your baby in a romper as soon as they’re born! In fact, a lot of parents like to put their babies in rompers as soon as they come home from the hospital.

There are different types of rompers for different seasons, though. You’ll want to get a lighter-weight romper for the spring and summer, and a heavier-weight romper for the fall and winter.

And sometimes you can find rompers that are water resistant or even waterproof, which is perfect for those days when it’s a little chilly outside but you don’t want to bundle your baby up too much.

Are 3 months the same as 0 to 3?

That’s a great question! The answer is…it depends. Most baby rompers are sized according to age, but there are a few that are sized according to weight. So it really depends on the specific romper.

But as a general rule, most baby rompers start at size 3 months and go up to 24 months. And if you’re not sure which size your baby needs, the best thing to do is to measure them.

What size is a 12-month onesie?

Well, that depends on the brand. Some brands go up to 18 months, while others only go up to 12 months. So it really depends on the brand you’re buying from.

But in general, a 12-month onesie is going to be pretty large. It’ll probably fit a baby who’s around 9 or 10 months old. So if you’re buying a onesie for a 12-month-old baby, you might want to go with something a little smaller.

Of course, there are always exceptions to the rule, so it’s always best to check the size charts. That’ll give you a better idea of what to expect.

Are rompers good for babies?

Some babies love rompers because they’re comfortable and easy to move around in. And they can be a great choice for a baby who’s constantly on the go.

But other babies might not like wearing anything tight around their bodies and might be more comfortable in clothes that allow them to move around more freely.

So it really depends on how you see the baby reacting to rompers. It’s best to get the right size and let them try and make a decision based on how they behave whenever you dress them up in rompers.


Finding the perfect baby romper size can be tricky, but with this comprehensive guide, you should be able to choose the right size every time.

Remember to measure your child’s chest, waist and inseam to find the best-fitting romper for your little one. And if you’re ever in doubt, we’re always here to help. Ask any questions you have in the comments and thanks for reading!

Picture in this post is by on Unsplash

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