Newborn nappies: meet Size 00 (and tips for babies under 4kg)Updated 5 days ago

Hi, I'm Morgan, Peachies Co-Founder. My son and daughter were both born at just 2.5kg, so nappies for newborns are close to my heart — and the reason we've launched Size 00.
A quick bit of context if this is all new: nappy sizes are based on baby's weight, not age. Getting the right size matters more than you'd think — too big and you'll get leaks, too small and you'll see red marks, pulled tabs, and an unhappy baby. The right fit means fewer changes and a lot more peace of mind in those first foggy weeks.

What is Size 00? Our new newborn nappy for babies 2.5 – 4kg. In the UK, that's where most newborns land — the average baby is born around 3.3 – 3.5kg, and 85% weigh between 2.5 – 3.9kg at birth. So while "newborn" might sound like a niche size, it's actually where most babies start.

Two features make Size 00 a game-changer for the early days:

• Umbilical cord cutout — a curved dip at the front so nothing rubs the cord while it heals (usually the first 1–2 weeks).
• Overlapping tabs — they fasten across the front for a snug, secure fit on the tiniest waists. Honestly, these made all the difference for my daughter Zoe.

How do I get it?

• Full Size 00 box — all Size 00. Best if baby is comfortably under 4kg.
• Mixed box — half Size 00, half Size 01. Ideal if baby is close to 4kg, growing fast, or you're not sure yet.

Most babies are in Size 00 for less than a month — the mixed box bridges that early stretch so nothing goes to waste.

Tips for the early days

• Newborn poo is… a lot. Frequent changes are normal in the first 2–3 weeks.
• In Size 01? Fold the front of the nappy down until the umbilical cord heals.
• Watch the tabs. Pulled to the edges or red marks on the thighs? Time to size up.
• Leaks at the back? Usually a sign the nappy's too small, not too big.

Still have questions? Our Concierge Team is one email away: [email protected].