Newborn sizes, without the guesswork
Why 0–3M is almost always the right first buy, and how to read a label in ten seconds.
Ayesha RazaBaby Ocean product team · August 28, 2026 · 5 min read
Baby sizing is measured in months, but babies are not. A label is a rough guide to length and weight, and length is the one that matters.
Read weight first, months second
0–3M usually covers 3.5 to 6 kg. Most newborns arrive inside that range, and grow out of it around eight weeks. If you only buy one size before birth, buy this one — and buy fewer pieces than you think you need.
What a first wardrobe actually looks like
Zips beat buttons at 3am
A two-way zip sleepsuit opens from the bottom for a nappy change without undressing the whole baby. Ten poppers, in the dark, with one hand, is a different experience. Buy at least two zip pieces before you buy a tenth popper piece.
Everything you buy in newborn size gets about six weeks of use. Spend on the four pieces you will wash twice a week, not the ten you will photograph once.
If in doubt, size up
- Sleeves and legs can be rolled — a tight neckline cannot be fixed.
- Cotton shrinks slightly on the first wash. Assume half a size.
- For mom wear, order one size above pre-pregnancy for the first eight weeks.
Easy first buys
More from the journal
Weeks 30 to 36: a two-week-at-a-time plan
Everything that has to be ready before birth, broken into small weeks so none of it lands at once.
Read guide
The first forty days: what new moms actually need
A quiet plan for the six weeks after birth — set up once, so the days ask less of you.
Read guide
Feeding at 3am: setting up so it is easier
Night feeds are not a problem to solve. They are a routine to make shorter and warmer.
Read guideTurn this guide into a kit
The hospital bag, newborn clothing and first-30-days lists are all available as kits you can edit piece by piece.