Choose collar size (in inches or cm) or letter size (S–XXL) first — collar size is anchored to an actual neck measurement, letter size is a brand's bundled label. Then pick your size in any system to see it in the others.
Wrap a soft tape measure around the base of your neck, roughly where a buttoned collar would sit, snug but not tight — then add about half an inch (1.3 cm) so the collar isn't choking. Round up to the nearest size on the chart if you land between two; a slightly loose collar is far more comfortable than a tight one.
Collar size is the exception in this whole category: the EU centimeter figure really is just the US/UK inch measurement times 2.54 — a 15" collar is 38.1 cm, a 16" collar is 40.6 cm. It's one of the only conversions here anchored to a real, brand-independent measurement rather than a marketing label.
The catch is rounding: a 15.5" collar works out to 39.4 cm, which sits almost exactly between EU 39 and EU 40 — some brands round down, some round up, so this chart lists it as "39/40" rather than picking one. Letter sizes (S–XXL) bundle collar size together with chest and sleeve length into one brand-chosen label, which is why they're marked approximate here even though the numeric collar size above them is close to exact.
| US / UK (in) | EU (cm) | Collar measurement |
|---|---|---|
| 14 | 36 | 35.6 cm |
| 14.5 | 37 | 36.8 cm |
| 15 | 38 | 38.1 cm |
| 15.5 | 39/40 | 39.4 cm |
| 16 | 41 | 40.6 cm |
| 16.5 | 42 | 41.9 cm |
| 17 | 43 | 43.2 cm |
| 17.5 | 44/45 | 44.5 cm |
| 18 | 46 | 45.7 cm |
| Letter | US collar (in) | EU collar (cm) |
|---|---|---|
| S | 14-14.5 | 36-37 |
| M | 15-15.5 | 38-40 |
| L | 16-16.5 | 41-42 |
| XL | 17-17.5 | 43-45 |
| XXL | 18 | 46 |
Letter sizes bundle collar, chest, and sleeve length together — the numeric collar size above is the more precise figure.
A 15.5" collar is 39.4 cm, which different brands round to either EU 39 or EU 40 — check the specific brand if you're between the two.
Wrap a soft tape measure around the base of your neck where a buttoned collar would sit, snug but not tight, and add about half an inch (1.3 cm) for comfortable movement. Round up to the nearest size on the chart if you're between two.
Approximately — but letter sizes bundle collar, chest, and sleeve length together in one brand-chosen label, so two shirts marked M can have different actual collar measurements. The numeric collar size is the more precise figure.