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How to Size Up Baby Clothing

5 min read | 10 December 2023

Parenthood is full of unexpected moments, but your baby growing out of their clothes isn’t one of them.

Finding the perfect fit for your little one can be challenging, especially as they grow so fast. And whether you’re a first-time parent or have been here before, there are plenty of questions to ask.

How many baby clothes do I need for each size? When is it okay to upsize? And how often will I be buying clothes? Today, we answer all these — and more — in the Purebaby guide to baby clothes sizes.

The baby clothing size guide: how it works

Like our adult garments, baby clothing sizes can vary drastically between brands. So, it’s never ideal to shop solely on size. Usually, you can determine the best fit for your baby by checking their height and weight against the measurements of the item. Purebaby offers a fit assistance tool on their website which can easily calculate this for you.

There is an age guide given by most brands, these are:






0-3 months old


3-6 months old


6-12 months old


12 months old


2 years old


3 years old


4 years old


5 years old

However, every baby is unique. So, if you find these sizes aren’t right for your little ones, let your baby guide you rather than relying on a baby clothes size chart by month.

Baby’s growth rates also differ, so when you’ll need to move up to the next size isn’t always the same. Most babies, though, can expect to grow through a few different sizes in their first six months alone.

From there, you’ll probably also wonder how many baby clothes in each size you’ll need. Babies tend to go through many dirty onesies and singlets during these early months. Depending on how often you plan to wash, you’ll need at least two or three outfits daily.

Before you know it, they’ll have grown out of the growsuit that used to be a little big on them and be ready to upsize.

How to tell if your baby needs to go up a size

Is your little one ready to drop a zero and try on some new clothes? While a baby clothing size chart is a good indication of the size they will need, you can also look for these tell-tale signs:

  • Closures won't close:

    When the snaps or buckles on your baby’s clothes become a struggle to close, it’s likely because they’ve outgrown that piece.

  • Elastic band marks on their skin:

    The elastic waistband on your baby’s pants may leave an indent on their stomach if they’re too tight. If you spot a red mark or line on their tummy or back, they may need to move up a size.

  • Clothes rolling over their belly:

    A top that rolls up and over a baby’s belly could indicate that it no longer fits. It should no longer be a problem with a longer and broader shirt.

The ins and outs of upsizing

With all this rapid growth, it’s always advisable to dress your baby in clothes that are one size too big. Sure, they might be a little baggy at first, but you’ll get more use out of them, and before you know it, they’ll be a perfect fit.

And while it seems like your little one never stops growing, the temptation to buy clothes that are a lot bigger is real. However, it’s best not to dress them in anything larger than one size up.

As well as the comfort factor, putting your baby in clothes that are too big for them can be unsafe. With the potential for fabrics to cover their face or head, especially in sleepwear, they need clothes that fit them properly. If you do plan to upsize further, stick with the pants and socks.

How Purebaby can help

Cuteness aside, shopping for new baby clothes can be overwhelming. So, take the guesswork out of it.

Purebaby’s baby clothes size chart is the only online fit assistant you need. You can match your baby's height, weight, age, and even head circumference to guarantee the correct size.

Shop our beautiful range of baby clothes today and guarantee the perfect fit for your little one.

Sign up to Pure Love Rewards and get $10 off your first online order, earn points every time you shop and more!

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If you need help selecting a size, please refer to our size chart.

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