UK to US Kids' Clothing Size Conversion
| UK Age | US Age |
|---|---|
| 2-3 | 2T |
| 3-4 | 3T |
| 4-5 | 4 |
| 5-6 | 5 |
| 6-7 | 6 |
| 7-8 | 7 |
| 8-9 | 8 |
Sizing conventions vary by brand and by cut — this table shows the standard published conversion. Always check the garment's own size chart when one is available. See how these tables are compiled.
Converting one imprecise age system into another
UK kids' clothing commonly labels sizes with an age range (5-6 years, 7-8 years), while US sizing often uses a single age-based number — converting UK to US age labels feels straightforward on the surface, but both systems share the same core limitation: an age assumption is a looser proxy for fit than a direct height measurement, so this conversion is matching two approximations rather than one precise figure to another.
A UK '5-6 years' range doesn't map onto one single US age number cleanly, since American labeling conventions vary by brand in exactly how they split a similar age bracket — some US brands might label the equivalent garment a '5', others a '6', both reasonably defensible interpretations of the same UK age range.
Height figures cut through the ambiguity better than age does
Where a US retailer publishes an approximate height range next to its age label (increasingly common, precisely because the age label alone is known to be unreliable), matching your child's actual height against that figure is more useful than trying to convert the UK age range through an assumed age-to-age correspondence.
Cut differences layer on top of the labeling question
British kids' clothing, especially school-adjacent categories like polo shirts and trousers, is sometimes cut with extra room for layering underneath, given British weather conventions, more so than typical American casual kids' wear — a UK size converted to a US age number can end up feeling smaller in that specific category once the layering allowance is accounted for, since American basics don't build in the same assumption.
What actually settles a first US order for a UK size
Measure your child's actual height and compare it to the specific US retailer's stated height range where published, rather than trusting a direct UK-age-to-US-age conversion, and expect UK school-adjacent garments specifically to run a bit roomier than the equivalent American item once layering allowance is factored out.
American winter wear leans toward different insulation choices
US kids' winter clothing more commonly uses synthetic insulation (puffer-style jackets) as the mainstream default, while UK winter kids' wear leans more toward wool or brushed-cotton layering pieces — this affects overall bulk and how a converted size feels more than the size-number conversion itself does, so expect a different silhouette even at a correctly converted age label for winter-specific garments.
Frequently asked questions
Does UK '5-6 years' convert to one specific US age number?
Not cleanly — US brands vary in exactly how they split a similar age bracket, so the equivalent garment might be labeled a US 5 by one brand and a US 6 by another, both reasonable interpretations of the same UK range.
Is age-to-age conversion reliable for kids' clothing generally?
Less reliable than most conversions on this site, since both the UK and US labels are approximations of an average child at that age — a height-based match is more precise where the figure is available.
Why might a UK school-adjacent garment feel roomier when converted to a US size?
Some UK brands cut categories like polo shirts and trousers with extra room for layering underneath (a jumper, given British weather), an allowance that typical American casual kids' basics don't build in the same way.
Should I use my child's height instead of the UK age label?
Yes, where available — matching actual height against a US retailer's stated height range is more reliable than converting the UK age range through an assumed age-to-age correspondence.
How current does my child's measurement need to be for this conversion?
As current as possible — children can move between size ranges within a few months during active growth, faster than either country's age-label system accounts for.
Does UK winter clothing convert the same way to US sizing as lighter garments?
The size-number logic is the same, but American winter wear leans toward puffer-style synthetic insulation as a mainstream default, while UK winter wear favors wool or brushed-cotton layering, affecting overall bulk and silhouette independent of the converted size.