How this instrument works
US and UK men's shoe sizing share the same underlying step — both scales move by one full size per third of an inch (a 'barleycorn') of foot length — but they're anchored at different starting points. That shared step is exactly why the conversion between them is a simple constant offset rather than a more complicated formula: US Men's size is always UK size plus 1, across the whole practical adult range.
This calculator applies that offset directly. Enter a UK size and it adds 1 to return the US Men's equivalent — no foot measurement required, since both scales already encode the same physical foot length, just numbered one apart. A UK 9 shoe and a US Men's 10 shoe are built to the same last length.
This is a Men's-sizing conversion specifically, using the same fixed-offset convention as this site's companion shoe-size tools (US-to-EU and US-to-UK). Women's and children's UK-to-US conversions use different offsets — women's sizing typically shifts by more than one full size between the two countries — so treat this one as scoped to men's shoes, the scale most UK retailers list by default on men's footwear.
- Find the UK size printed on the shoebox or the shoe's own size tag.
- Enter that UK size into the calculator.
- Read the equivalent US Men's size — UK size plus 1.
- If you're shopping a US site with a UK-labeled shoe in hand, use this US figure to pick the matching size from the dropdown.
Worked example — a UK 9 boot ordered from a US retailer
A pair of boots bought in a UK shop is sized UK 9 on the box. Ordering a matching pair from a US retailer's website, which only lists US Men's sizes in its dropdown, means converting first: US Men's size = 9 + 1 = 10.
The same offset applies at any size, including half sizes — a UK 11.5 becomes a US Men's 12.5, and a UK 7 becomes a US Men's 8. Because it's a flat +1 across the whole range, there's no need to look up a size chart table for each individual size; the single formula covers all of them.
Questions
Is US Men's size always exactly UK size plus 1?
Yes, for the standard men's sizing convention used across most brands and retailers, US Men's = UK + 1 holds across the practical adult range. Some individual brands cut their lasts slightly differently and may be off by a half size from this convention, but the +1 offset is the industry-standard reference point used on nearly every general shoe-size conversion chart.
Does this conversion work for women's shoe sizes?
No — this calculator is scoped to men's sizing specifically. Women's UK-to-US conversion uses a different, larger offset (commonly UK + 2 rather than UK + 1), since men's and women's US sizing itself is offset even for an identical foot length. Using the men's formula on a women's UK size will give the wrong US size.
Why is the UK size always the lower number?
It's purely a historical numbering convention, not a reflection of actual shoe size — UK sizing happens to start its count one size lower than US sizing for the same physical foot length. Neither system is 'more accurate' than the other; they just use different reference points for what counts as size 1.
How does this relate to EU shoe sizes?
This site has a separate US-to-EU converter using the constant offset EU = US Men's size + 33 (anchored at US9=EU42). Combining the two: a UK size converts to US via +1, and that US figure converts to EU via +33, giving a full UK-to-EU chain if you need it.
Should I round to the nearest half size, or size up if I'm between sizes?
This calculator returns the exact converted figure, including half sizes. If your foot measures between two sizes in practice, sizing up half a size is the more common recommendation for comfort, particularly for closed-toe shoes, but that's a fit preference rather than part of the conversion math itself.