Hat Size Conversion Chart
Convert US and UK fitted hat sizes, European centimeter sizes and S/M/L from head circumference.
A US fitted hat size is the head circumference in inches divided by π. A 56 cm head is 22 inches around, which is a US 7, a UK 6⅞ and a European 56.
By Piero Nanni · Last checked
Matching rows are highlighted in the tables below.
Hat sizing is the rare case where the odd-looking traditional numbers are derived rather than arbitrary. A US fitted size is the head circumference in inches divided by π, which is to say it is the diameter of the head treated as a circle. A 7⅛ hat fits a head 22⅜ inches around.
The European system skips the arithmetic and states the circumference in centimeters, so a 58 cm hat fits a 58 cm head. The UK uses the same derived numbers as the US but runs one eighth smaller, a difference of about half a centimeter, which is enough to matter in a stiff hat and not enough to notice in a soft one.
Hat sizes by head circumference
Measure around the head about 1 cm above the ears and across the middle of the forehead.
| Head (cm) | Head (in) | US | UK | EU | Letter |
|---|---|---|---|---|---|
| 53 | 20⅞ | 6⅝ | 6½ | 53 | XS |
| 54 | 21¼ | 6¾ | 6⅝ | 54 | S |
| 55 | 21⅝ | 6⅞ | 6¾ | 55 | S |
| 56 | 22 | 7 | 6⅞ | 56 | M |
| 57 | 22½ | 7⅛ | 7 | 57 | M |
| 58 | 22⅞ | 7¼ | 7⅛ | 58 | L |
| 59 | 23¼ | 7⅜ | 7¼ | 59 | L |
| 60 | 23⅝ | 7½ | 7⅜ | 60 | XL |
| 61 | 24 | 7⅝ | 7½ | 61 | XL |
| 62 | 24¼ | 7¾ | 7⅝ | 62 | XXL |
| 63 | 24¾ | 7⅞ | 7¾ | 63 | XXL |
| 64 | 25¼ | 8 | 7⅞ | 64 | XXXL |
The formula
US hat size = head circumference in inches ÷ π. Measure 22 inches around and the size is 22 ÷ 3.14159 = 7.00. Measure 23¼ inches and it is 7.40, which rounds to the 7⅜ on the label.
Sizes step in eighths, and an eighth of a size is about 1 cm of circumference, so the granularity is coarser than it looks. Between two sizes, take the larger and use a sizing tape inside the band; a hat that is slightly loose can be padded, while one that is tight cannot be fixed.
Measuring a head
Run the tape around the widest part: about a centimeter above the eyebrows and ears, and over the bump at the back of the skull. Keep it level and snug but not tight, the way the hat will actually sit.
Measure over the hair as you normally wear it. A measurement taken with the hair up or wet will be wrong by enough to change the size, and long hair worn down can add a full centimeter.
Fitted, snapback and stretch
Only fitted caps and traditional hats use these numbers. Snapbacks and adjustable caps are one size with a range of roughly 55 to 61 cm, and stretch-fit caps are sold as S/M and L/XL covering about 3 cm each.
Straw and felt hats can be stretched slightly by a hatter, and felt can be shrunk, so a traditional hat has a little adjustment in it. A fitted baseball cap has none, which is why its sizing is the strictest of the lot.
Frequently Asked Questions
What size hat is a 58 cm head?
A 58 cm head is a US 7¼, a UK 7⅛ and a European 58, which is a large.
How do I calculate my hat size?
Measure your head circumference in inches and divide by π (3.14159). That figure is the US fitted size.
What is a size 7 hat in cm?
A US size 7 fits a head of about 56 cm, or 22 inches around.
Are UK and US hat sizes the same?
No. A UK size is one eighth smaller than the US size for the same head, about half a centimeter.
What is the most common hat size?
Around 57 to 58 cm, which is a US 7⅛ to 7¼, or a medium to large.