You find the perfect baby outfit online, and then the sizing stops you cold: is “62” a real size? Is a US “3M” the same as a UK “0–3 months”? Why does one brand's 6-month fit like another's 9-month? Baby clothing sizes are labelled differently across the US, UK, and Europe, and the systems don't line up neatly — which makes shopping across brands or borders genuinely confusing. Here's how the three systems compare, and the one rule that cuts through all of it.
The Three Systems, Briefly
- US: Labelled by age in months and years — Newborn, 3M, 6M, 9M, 12M, 18M, 24M (or 2T).
- UK: Also by age, but usually as a range — “Newborn,” “0–3 months,” “3–6 months,” “6–9 months,” and so on.
- EU: Labelled by the baby's height in centimetres — 50, 56, 62, 68, 74, 80, 86. This is the one that confuses people, but it's arguably the most useful, because it's based on the body, not an assumed age.
So a European “62” isn't a mystery — it means the garment fits a baby around 62cm tall.
The Rough Conversion Chart
Approximate equivalents (always a guide, never exact):
- US Newborn ≈ UK Up to 1 month ≈ EU 50–56 (baby ~2.5–4 kg)
- US 3M ≈ UK 0–3 months ≈ EU 56–62 (~4–5.5 kg)
- US 6M ≈ UK 3–6 months ≈ EU 62–68 (~5.5–7.5 kg)
- US 9M ≈ UK 6–9 months ≈ EU 68–74 (~7.5–9 kg)
- US 12M ≈ UK 9–12 months ≈ EU 74–80 (~9–10.5 kg)
- US 18M ≈ UK 12–18 months ≈ EU 80–86 (~10.5–12 kg)
- US 24M / 2T ≈ UK 18–24 months ≈ EU 86–92 (~12–13.5 kg)
Notice the US and UK labels are offset: a US “6M” roughly matches a UK “3–6 months,” because the US label often marks the top of the range and the UK marks the range itself. This single offset is behind most cross-brand confusion.
The One Rule That Cuts Through It All
Ignore the label system and shop by your baby's weight and height. Every reputable brand — whatever country it's labelled for — publishes a size chart with weight and height ranges. Those numbers are universal; “6M” is not. Measure your baby's height and know their rough weight, then match to the chart rather than trusting the age on the tag. This is the only reliable way to buy across brands and borders (see our baby clothes size chart).
Why the Systems Disagree Anyway
- Age labels assume an “average” baby, and no baby is average — so the same age fits differently child to child.
- Brands cut differently. Even within one country, one brand's 6M runs bigger than another's — which is why the conversion is always “approximate.”
- The EU height system is the most precise, because it's tied to the body — if you can find the height label, it's often the most reliable of the three.
Practical Tips for Buying Across Systems
- Always check the brand's own weight/height chart before ordering — don't assume “6M is 6M” across brands.
- Know your baby's current height and weight, and keep them handy when shopping.
- Size up when between — a roomy piece lasts longer than a snug one (see our guide to moving up a size).
- Use the EU height label as a tiebreaker when age labels conflict — it's the most body-based number.
- Check the returns policy when buying a brand new to you, until you know how it runs.
The Bottom Line
US, UK, and EU baby sizes use different systems — US by age, UK by age range, EU by height in centimetres — and they don't line up exactly, with the US/UK offset causing most of the confusion. The fix is simple: shop by your baby's weight and height against each brand's own chart, treat the age label as a rough hint, and use the EU height number as the most reliable guide. Do that and “what size is a 62?” stops being a problem, wherever you're buying from.
Check our size chart for weight and height ranges, and browse our collections — sized to fit babies wherever you are.