Shirt collar calculator
Enter your neck circumference to find your collar size.
Shirt collar size is measured by the neck circumference in centimetres. The French system uses this value directly: size 40 = 40 cm neck (measured with slight ease). The US system uses inches. A French size 40 equals a US collar 15¾.
Measure your neck at the base, just above the Adam's apple where it meets the shoulders. Slip a finger under the tape for comfort. A shirt too tight restricts circulation and pushes the tie up. If between sizes, take the larger one.
- Take a soft tape measure.
- Place it around the neck base, just above the Adam's apple.
- Slip one finger under the tape for comfort.
- Note the measurement in centimetres: that is your collar size.
| Neck circumference (cm) | FR collar (cm) | US collar (inches) | Letter size |
|---|---|---|---|
| 34-35 cm | 35 | 13½" | XS |
| 36-36 cm | 36 | 14" | XS |
| 37 cm | 37 | 14½" | S |
| 38 cm | 38 | 15" | S |
| 39 cm | 39 | 15½" | M |
| 40 cm | 40 | 15½" | M |
| 41 cm | 41 | 16" | L |
| 42 cm | 42 | 16½" | L |
| 43 cm | 43 | 17" | XL |
| 44 cm | 44 | 17½" | XL |
| 45 cm | 45 | 17¾" | XXL |
| 46+ cm | 46 | 18" | XXL+ |
Frequently asked questions
How do I convert a US size to a French size?
Multiply the US size by 2.54 (1 inch = 2.54 cm). Example: US 16 collar = 40.6 cm = French size 40. Our table provides the direct correspondence for common sizes.
What size for a dress shirt vs a casual shirt?
For a dress shirt (with tie), take your exact size. For a casual shirt worn open-collar, you can go one size down for a tighter fit.
How do I know if my shirt is the right size?
When fully buttoned, you should be able to slide one finger between your neck and collar without discomfort. If the collar restricts you, size up.
What do letter sizes (S, M, L) correspond to?
S = 37-38 cm, M = 39-40 cm, L = 41-42 cm, XL = 43-44 cm, XXL = 45-46 cm. Letter sizes are approximate; neck circumference in cm remains the precise reference.