The collar number on a dress shirt, such as 15½ or 39, is the size of the neck the collar fits. It is the first number most men look for when shopping for shirts, and the one that causes the most returns, because it is not the same as the neck you measure. This calculator takes your neck measurement and the ease you want, and gives the collar size to buy, in inches and centimetres.
How to use the collar size calculator
- Measure your neck at the height where the collar sits, just below the Adam’s apple, standing relaxed. Do not crane the neck out or tuck the chin in.
- Choose the ease: half an inch is the usual allowance.
- Enter both in inches or centimetres.
- Read the collar size, the nearest size sold in half inches, and the matching S–5XL size.
Collar size formula
cm = inches × 2.54 (shops round to 37, 38, 39, 41 …)
ease: ½ inch (Hawes & Curtis), one finger (Proper Cloth), two fingers (Charles Tyrwhitt)
The measuring advice comes from Hawes & Curtis, Proper Cloth, Charles Tyrwhitt and Turnbull & Asser, and the sizes from T.M. Lewin and Marks & Spencer (all retrieved 2026-10-15). T.M. Lewin sizes jump by 1 inch above 18, so a neck of 18½ becomes a 19.
| Collar (in) | Collar (cm, T.M. Lewin) |
|---|---|
| 14.5 | 37 |
| 15 | 38 |
| 15.5 | 39 |
| 16 | 41 |
| 16.5 | 42 |
| 17 | 43 |
| 17.5 | 44 |
| 18 | 46 |
| 19 | 48 |
| 20 | 51 |
| M&S size | Neck (cm) | Neck (in) | Chest (in) | Sleeve (in) |
|---|---|---|---|---|
| S | 36–37 | 14–14.5 | 34–36 | 34–34.5 |
| M | 38–40 | 15–15.5 | 38–40 | 35–35.5 |
| L | 41–42 | 16–16.5 | 42–44 | 36–36.5 |
| XL | 43 | 17 | 46 | 36.5 |
| 2XL | 44–46 | 17.5–18 | 48–50 | 37–37.5 |
| 3XL | 47–48 | 18.5–19 | 52–54 | 37.5–38 |
| 4XL | 49–50 | 19.5–20 | 56–58 | 38–38.5 |
| 5XL | 52–53 | 20.5–21 | 60–62 | 38.5–39 |
Worked example
A neck of 15 inches with the standard half inch of ease.
- 15 + 0.5 = 15.5, already on a half inch → collar 15.5 in.
- T.M. Lewin sells a 15½ collar, which is 39 cm.
- On the M&S chart this is a M (neck 15–15.5 in).
Checking the fit
- Finger test: you should be able to slip a finger between a buttoned collar and your neck.
- Shrinkage: cotton shirts shrink slightly, and Turnbull & Asser say they build in up to half an inch.
- With a tie: a collar that fits with the top button done up will feel tighter once a tie is knotted.
- Measure a shirt: measuring the collar of a shirt that fits you well is the most reliable check.
Pair the collar with the sleeve using the Sleeve Length Calculator, and see the Shirt Size Calculator for casual shirts. This page is general guidance.
Sources
Every figure above comes from these pages, read directly on the dates shown. Brand names are used only to identify published charts.
- Hawes & Curtis — how to measure (neck + ½ inch) — checked 2026-10-15
- Charles Tyrwhitt — how to measure for a shirt (collar and sleeve) — checked 2026-10-15
- Proper Cloth — dress shirt body measurements (neck, sleeve) — checked 2026-10-15
- Turnbull & Asser — shirt size guide (collar allowance, shrinkage) — checked 2026-10-15
- T.M. Lewin — shirt size charts (collar sizes in inches and cm) — checked 2026-10-15
- Marks & Spencer — formal shirts size guide — checked 2026-10-15
Frequently asked questions
How do I measure my collar size?
Place a tape around your neck at the height where the collar would sit, just below the Adam’s apple, relaxed. Hawes & Curtis says to measure around the neck and add half an inch; Proper Cloth says to hold one finger behind the tape; Charles Tyrwhitt suggests two fingers for the most comfortable fit.
Why add ease?
A collar that is exactly your neck size is uncomfortable once buttoned with a tie. A small allowance gives room to breathe. The calculator lets you choose the ease, with half an inch as the default.
Why does my collar size not match the neck I measured?
Collar sizes are the length of the collar band, not the neck. Turnbull & Asser notes that the actual collar measurement on a new shirt can be up to half an inch larger than the stated size because shirts shrink in the first washes.
What are the standard collar sizes?
T.M. Lewin sells collars of 14½, 15, 15½, 16, 16½, 17, 17½, 18, 19 and 20 inches, which are 37, 38, 39, 41, 42, 43, 44, 46, 48 and 51 cm. The calculator rounds your size up to the next one sold.
How does collar size relate to S, M and L?
On Marks & Spencer’s formal shirt chart a small fits a 14–14½ inch neck, a medium 15–15½, a large 16–16½ and an XL 17. See also Shirt Size Calculator and Sleeve Length Calculator.