Men's Suit & Hat Size Converter
Convert a US/UK suit or jacket size to its EU equivalent, and convert head circumference to a hat size in US numbering, centimeters, and general S/M/L/XL.
Suit & jacket size (US/UK → EU)
= EU 50
International shoe size converter
UK: 9.5
EU: 44
CM / JP: 28.0
Hat size (head circumference)
US hat size: 7
General size: M
Quick-reference suit size chart
Men's & Women's international shoe size guide
Suit sizing uses the standard EU = US/UK + 10 convention (US 40R = EU 50). Shoe sizes vary slightly across shoe lasts and sneaker vs. dress shoe brands. Hat sizing converts circumference using circumference (inches) ÷ π.
About this tool
How to use it
- For a suit or jacket, enter your US or UK size number in the first panel to see its EU equivalent.
- For a hat, enter your head circumference in either centimeters or inches in the second panel — the other unit fills in automatically, along with a US hat size and a general S/M/L/XL band.
- Press Convert, or just keep typing — both panels update live.
- Check the quick-reference chart below for common suit sizes without typing anything.
Why it matters
Suit and hat sizing use completely different numbering systems country to country and maker to maker, so a size that fits at home can be a confusing set of unfamiliar numbers when shopping from an overseas retailer's chart. Converting the numbers directly removes the guesswork of matching an unfamiliar sizing system to the one you already know.
When to use it
Useful when buying a suit, jacket, or hat from an international retailer whose size chart uses a different numbering convention than you're used to, or when checking your own measurements against a chart before ordering online.
Good to know
Suit sizing uses the widely-cited EU = US/UK + 10 convention, which most menswear retailers follow closely but not universally — some brands run their EU sizing a size or two off this formula, so it's worth checking a specific brand's own chart when the fit really matters. Hat sizing converts head circumference to a US hat number using circumference (inches) ÷ π, the traditional formula hat makers use, rounded to the nearest eighth of an inch (the standard hat-size increment); the S/M/L/XL 'general size' band is an approximate common guide, not a single agreed industry standard, since retailers' own bands can vary by a centimeter or two.
Common questions
Is a US 40 jacket the same as a UK 40?
Yes — US and UK men's suit and jacket sizing use the same number system (a US 40R and a UK 40R are the same size), unlike EU sizing, which typically runs 10 higher than the US/UK number for the same fit.
How is hat size calculated from head circumference?
Divide your head circumference in inches by π (about 3.14159) — this is the traditional formula hat makers use, since a hat's labeled 'size' has historically referred to its inside diameter, and circumference = π × diameter. The result is rounded to the nearest eighth of an inch, the standard increment hat sizes are sold in.
Why do S/M/L/XL hat sizes vary between websites?
There's no single universal standard mapping circumference to letter sizes — different retailers and hat makers use their own bands, sometimes differing by a centimeter or more at the boundaries. Use the letter size shown here as a general starting point, but check the specific retailer's own size chart for anything close to a boundary.
How do I measure my head circumference accurately?
Wrap a soft tape measure around your head about an inch above your eyebrows and ears, at the widest point, keeping the tape snug but not tight. Measuring at a slightly different height can change the reading by a centimeter or more, which is enough to shift the result to a different general size band.