Hat Size Chart: US Fitted Sizes, UK Sizes and Centimeters
For anyone ordering a fitted cap, fedora or beanie without trying it on. The chart converts every US, UK, metric and letter size, and explains what the fractional numbers actually mean.
Hat size is based on head circumference, measured about 1/8 in above the ears. US fitted size 7 1/4 equals 58 cm (22 3/4 in), and each 1/8 step changes the circumference by about 1 cm (3/8 in). European sizes are simply the circumference in centimeters.
- US 7 1/4
- 58 cm / 22 3/4 in
- One 1/8 size
- ≈ 1 cm (3/8 in)
- US to UK
- UK is 1/8 smaller
- Size M (typical)
- 56–57 cm
On this page
Hat size conversion chart
Find your head circumference in the inch or centimeter column, then read across. The inch and cm figures are calculated from each US size; the EU size is the same figure rounded to a whole centimeter. If you fall between two rows, take the larger size; a hat can be padded down with sizing tape but cannot be made bigger by much.
| US size | Head (in) | Head (cm) | EU size | UK size | Letter |
|---|---|---|---|---|---|
| 6 1/2 | 20.4 | 51.9 | 52 | 6 3/8 | XXS |
| 6 5/8 | 20.8 | 52.9 | 53 | 6 1/2 | XS |
| 6 3/4 | 21.2 | 53.9 | 54 | 6 5/8 | S |
| 6 7/8 | 21.6 | 54.9 | 55 | 6 3/4 | S |
| 7 | 22.0 | 55.9 | 56 | 6 7/8 | M |
| 7 1/8 | 22.4 | 56.9 | 57 | 7 | M |
| 7 1/4 | 22.8 | 57.9 | 58 | 7 1/8 | L |
| 7 3/8 | 23.2 | 58.8 | 59 | 7 1/4 | L |
| 7 1/2 | 23.6 | 59.8 | 60 | 7 3/8 | XL |
| 7 5/8 | 24.0 | 60.8 | 61 | 7 1/2 | XL |
| 7 3/4 | 24.3 | 61.8 | 62 | 7 5/8 | XXL |
| 7 7/8 | 24.7 | 62.8 | 63 | 7 3/4 | XXL |
| 8 | 25.1 | 63.8 | 64 | 7 7/8 | 3XL |
Letter sizes vary by brand. The pattern above (M = 56 to 57 cm, L = 58 to 59 cm) is common, but some cap makers sell two-size ranges such as S/M and L/XL that each span about 4 cm. Check the centimeter figure on the brand's chart, not the letter.
What the fractional sizes mean
US and UK hat sizes date from hatters who measured the head's length and width and averaged them. Today the size is derived from circumference: US size = head circumference in inches ÷ π. A 22-inch head divided by 3.1416 gives 7.0, so it wears a size 7.
That formula explains the odd steps. Each 1/8 of a size adds π/8 = 0.39 in to the circumference, which is 1.0 cm. Hatters round this to "one size per centimeter", which is why a 7 1/4 is listed as 58 cm and a 7 3/8 as 59 cm even though the exact calculation gives 57.9 and 58.8 cm.
UK makers apply the same idea to a slightly different baseline, so a UK size reads 1/8 lower than the US size for the same head. A British 7 1/8 and an American 7 1/4 fit the same person.
How to measure your head
- Use a soft tape measure. If you only have a string or a phone charging cable, mark it and lay it against a rigid ruler.
- Place it where the hat sits. Run the tape across the middle of the forehead, about 1/8 in (3 mm) above the eyebrows and the tops of the ears, and around the fullest part of the back of the head.
- Keep it level and snug. Pull it as firmly as a hat band would sit, without compressing hair. Thick hair, braids or a bun can add 1 to 2 cm, so measure the way you will wear the hat.
- Take two readings. If they differ, use the larger one, then find it in the chart above.
Most fitted caps and felt hats print the size on a label under the sweatband. If a hat you own fits well, its size is a more reliable guide than a tape measure, as long as you buy the same style.
Sizes by hat type
The circumference rule is the same for every hat, but the size range and the amount of give are not.
| Hat type | How it is sized | Fit notes |
|---|---|---|
| Fitted baseball cap | US fractional sizes, about 6 1/2 to 8 1/4 | Wool and polyester crowns stretch little; cotton caps can shrink slightly if washed hot |
| Snapback and strapback | One size, adjustable | Typically about 55–60 cm; strap adjusts the back opening |
| Stretch-fit cap | Two or three size ranges, e.g. S/M, L/XL | Each range covers about 3–4 cm via an elastic band |
| Fedora, trilby, felt hats | US/UK sizes or cm | Fit should be exact; sizing tape can take up about half a size |
| Straw hats, sun hats | S/M/L or cm, often with an inner drawstring | Straw does not stretch; size up if between sizes |
| Knit beanie | One size, or child/adult | Knit stretches about 15–25%; very large heads may want an XL or slouch beanie |
| Helmets | cm ranges per size | Safety fit is set by the helmet standard and maker's chart, not hat sizes |
Head shape matters as well as circumference. Oval heads (longer front to back) find round-crowned hats pressing at the forehead and back. Rounder heads find long-oval hats pinching at the sides. If a hat in your size presses in one place only, the issue is shape; a hatter can stretch felt locally, or you can try another brand's block.
Baby and children's hat sizes
Children's hats are sold by age, but heads grow fastest in the first year, so check the circumference when you can. The figures below are the World Health Organization median head circumferences for girls and boys (the lower and upper value of each range), with the age labels retailers use.
| Age | Head (cm) | Head (in) | Typical hat label |
|---|---|---|---|
| Newborn | 33.9–34.5 | 13.3–13.6 | Newborn / 0–3 months |
| 3 months | 39.5–40.5 | 15.6–15.9 | 3–6 months |
| 6 months | 42.2–43.3 | 16.6–17.0 | 6–12 months |
| 12 months | 44.9–46.1 | 17.7–18.1 | 12–24 months |
| 2 years | 47.2–48.3 | 18.6–19.0 | 2–4 years |
Individual children vary by a few centimeters either side of these medians. After age 2 the head grows slowly, by about 1 cm a year or less, and many children reach an adult S (54 to 55 cm) by their early teens. Baby knit hats stretch, so a 0–3 month hat fits most heads up to about 38 cm. For hair accessories sized on the same measurement, see the headband size guide.
Common sizing mistakes
- Measuring too low. A tape around the ear lobes or the neck end of the skull reads smaller than where a hat actually sits.
- Mixing UK and US charts. A British hatter's 7 1/4 is a US 7 3/8, which is a full centimeter bigger than many buyers expect.
- Assuming caps and hats match. A fitted cap's 7 1/4 and a fedora's 7 1/4 both mean 58 cm, but a cap sits higher on the head and a fedora lower, so many people wear different sizes in each.
- Ignoring hair. Long hair worn up, braids or locs can move you up one or two sizes.
To store hats without crushing the crown, see the hat box size guide. Cold-weather sets are covered in the scarf size guide and glove size chart.
Frequently asked questions
What do the numbers on fitted hats mean? Does 8 mean an 8-inch circumference?
No. A US hat size is roughly the head's circumference divided by π, so it behaves like an average head diameter in inches. Size 8 corresponds to a circumference of about 25 1/8 in (64 cm), and size 7 to 22 in (56 cm).
How do I convert hat size to centimeters?
Multiply the US size by 3.1416 to get inches, then by 2.54 for centimeters. For example, 7 3/8 × 3.1416 = 23.17 in, which is 58.8 cm, sold as 59 cm.
What is the average hat size?
Most adult men fall between 7 and 7 1/2 (56 to 60 cm) and most adult women between 6 3/4 and 7 1/4 (54 to 58 cm). That is why one-size adjustable caps are usually built around 7 1/8 to 7 3/8.
Are UK and US hat sizes the same?
No. For the same head, the UK number is 1/8 smaller: a 58 cm head is a US 7 1/4 and a UK 7 1/8. European sizes avoid the confusion because they use centimeters directly.
What hat size is one size fits most?
Adjustable and stretch caps labeled one size usually fit about 55 to 60 cm (US 6 7/8 to 7 1/2). Below that, look for youth or S/M sizes; above it, look for XL or XXL fitted caps.
Should a hat be tight or loose?
Snug but not pressing. You should be able to slide one finger between the sweatband and your forehead. A hat that leaves a red line after 10 minutes is too small; one that drops when you nod is too large.