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Transitioning through the zeros: Understanding baby sizing for size 0 baby

Viva Bianca

Viva Bianca

Viva is a writer, editor and mum (AKA professional snack bitch) – and not in that order. With a background in film, feminism and culture journalism, Viva brings her curiosity for storytelling to her role as Culture & Lifestyle Editor at Kiindred, and loves offering advice and tit-bits to other parents - it takes a village!
Created on Oct 22, 2023 · 4 mins read

Wardrobe shopping for someone you haven’t even met and whose birth size is yet to be determined can prove challenging. But in our information-overloaded reality today, this precious little mystery, waiting to reveal itself, can also be quite fun… Needless to say, if you’ve never shopped for baby clothing before, you’re probably quite confused about all the zeros!

We’ve partnered with H&M to help you understand the science behind baby sizing – and to give you the heads up about when to drop a zero!

Bear in mind that, like us, every baby will grow at slightly different stages and ages and so there’s no exact one-size-fits-all blueprint when it comes to babies and clothing sizes.


Size 00000

Yes, that’s a lot of 0’s! Size 00000 is for premature babies (about 2kg). Although you can’t normally know in advance if your baby will be born preemie, if you’re anticipating your baby’s grand earthside entrance at around 40 weeks (or a little over or under), you probably don’t need to buy this size.

Hint: It’s tiny! If your baby does surprise you with an earlier than expected arrival, you can always ask a family member or close friend to dash to H&M to pick up some 00000’s onesies and drop them off at the hospital.

Size 0000

This size is for newborns (around 3kg) and is the most common clothing size for the first month or so of a baby’s life. Definitely invest in some staple baby pieces (onesies, singlets, bodysuits, socks, pants/leggings) in size 0000, but remember, your baby will outgrow this size quicker than any other clothing size in their future wardrobe.

Also, be mindful that some babies are born much bigger than expected, so if your baby is born weighing around 4kg, they may well miss size 0000 altogether. Our advice is to not go overboard with your size 0000 collection. You may only get a few weeks (or none at all) out of them!


Size 000

Size 000 is designed for babies aged 0-3 months old (or around 6kg). You’ll probably get more mileage out of this size than size 0000, so feel free to buy more of each piece (onesies, singlets, bodysuits, socks, pants/leggings) in this size. Don’t worry if your baby is swimming in their size 000 onesie, to begin with; you can always roll up sleeves and waistbands. Your little one will grow into this size before you know it!

Size 00


Size 00 is for babies aged 3-6 months (or 4-7 months) and will be the first range of clothing your baby will likely make a big mess of! That’s because it’s about the age that they will be introduced to solids – and possibly even start exploring the house. So, by the time your baby has reached size 00, you might want to consider investing in some ‘play clothes’, which has the added benefit of expanding your baby’s wardrobe from onesies and bodysuits to overalls, tops and pants.

Size 0 

Size 0 is for a 9-month-old (roughly), so, because you can expect a lot of activity at this age from your little one (crawling, climbing, cruising, maybe walking, playing, eating), it would be a good idea to be prepared for numerous outfit changes a dayInvesting in several pairs of pants, tops, singlets, onesies and extra play clothes for this stage would be wise.

Tip: Choose clothes that won’t inhibit your baby’s will to explore – and the ability to learn to crawl and walk. Soft, stretchy organic cotton is ideal.

Size 1

What a milestone! You’ve spent an entire year with your bundle of joy, enveloping them with love, nurture, nutrition and guidance (and with all the sleepless nights, you’ve likely also aged about 5 years!). This is a fun age to shop for because if your baby hasn’t begun walking yet, they will probably begin to test the waters pretty soon.

That means it’s time for shoes and to start having a little fun with fashion – think skirts, dresses, chinos or overalls to enter the playing field. Oh to be a baby fashionista!


Bonus tips!

  • Buy gender-neutral/unisex clothing, where possible. If you’re planning on having more than one baby, your future self will be grateful.
  • Choose zips or press studs over buttons. Buttons are a nighttime nappy change headache!
  • Consider buying singlet suits, such as bodysuits, because they don’t ride up a baby’s body.
  • Envelope shoulder tops and bodysuits enable you to pull the garment down the baby’s body to remove it, so as to avoid having to pull any nappy leakages up over your baby’s head. Trust us, accidents will happen!

While there’s no exact one-size-fits-all blueprint when it comes to babies and clothing sizes, it’s a good idea to familiarise yourself with baby sizing and its accompanying ages/stages. That way you can shop with a little more street smarts 😉.

This is a paid partnership between Kiindred x H&M.

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