One of the most common men's sizes, a 101 cm chest is US 40 and the second body carried under INT M, so an M can mean a 96 or a 101 cm chest.
Brand fit: British waists average near 86 cm, up about 16 cm since 1951, so at this 101 cm chest an average belly lands at the centre of the M waist band (81-91), well above where a trim-cut 40 sits.
UK to US conversion
British and American men's jacket sizes are the same number, so UK 40 is US 40 and UK 46 is US 46 with nothing to convert. Both label the chest in inches, which is why the columns match and the site keeps a single page for the pair rather than a reverse. The catch is that neither number is tightly standardised, so a UK 40 and a US 40 from two makers can each measure a couple of inches off the nominal chest.
At this size, UK to US
One size up from UK 40, US moves 2 to US 42 while UK rises 2 to UK 42, holding their spacing. Both UK 40 and US 40 are whole numbers here, so nothing rounds. For UK 40, the US column here runs US 38, US 40, US 42, stepping two numbers at a time.
Size Chart UK US EU INT 34 34 44 XS 36 36 46 S 38 38 48 M 40 40 50 M 42 42 52 L 44 44 54 L 46 46 56 XL
Frequently Asked Questions Does UK 40 round up or down in US? Round to the chest for a jacket and to the larger figure if chest and waist disagree; a drop-two cut assumes a smaller waist, which not every body follows.
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Note UK and US men's sizes are typically identical EU sizes are approximately UK + 10 Fit varies by garment type - jackets vs shirts vs casual Clothing sizes vary significantly by brand See a number that looks off? Report an error on this page.