Hat Size Calculator
Measure the circumference of your head at the widest point, enter it below, and this calculator instantly converts it to your US, UK, EU and international letter hat sizes. Switch between centimetres and inches; results update as you type.
How to measure your head for a hat
You need a soft tape measure or a length of string and a ruler. Wrap the tape around the widest part of your head, roughly 1 cm (about half an inch) above your ears and across the mid-forehead, at the position where your hat will actually sit. Hold the tape snug but not tight, it should not compress your hair. Take the reading in centimetres or inches and enter it above. If you only have a string, mark it where the ends meet, then measure that length with a ruler. Measure twice: heads are not perfectly round, so the same head can give a reading that varies by a centimetre between attempts. Use the larger of the two readings.
How hat sizing systems work
There are three main hat sizing systems in use today. The EU system is the simplest: your hat size equals your head circumference in centimetres, rounded down. A 57.4 cm head is EU size 57. The US system divides head circumference in inches by pi and rounds to the nearest eighth of an inch. So 22.5 inches divided by 3.14159 gives roughly 7.16, which rounds to 7 1/8. The UK system is identical to the US system except it runs one-eighth of an inch smaller than the US size. This means a US 7 1/8 and a UK 7 are often the same physical hat. International letter sizes (S, M, L and so on) are loose bands that cover a range of 2 centimetres each, so they do not give a precise fit. Always use your numeric EU or US size when buying a fitted hat.
What to do when you are between sizes
Hat sizes increase in discrete steps of 1 cm (EU) or 1/8 inch (US/UK). If your measurement falls between two bracket values, always choose the larger size. A hat that is slightly too large can be made to fit with foam hat-size reducers, fabric strips, or hat tape applied to the inside sweatband. These typically add 0.5 to 1 cm of effective circumference. Trying to stretch a hat that is too small risks damaging the shape. For felt and structured hats, a professional hatter can stretch a hat by 0.5 to 1 size on a hat stretcher.
Differences between hat types and brands
Not all hats of the same size label fit the same way. The shape of the crown matters: a round oval crown fits round heads best, while an oval crown suits people whose heads are longer front-to-back than side-to-side. Many brands mark their hats as "long oval," "round oval," or "oval." Baseball caps and bucket hats are often sold in Small/Medium/Large bands rather than exact sizes, and the ranges vary by brand. Fedoras and structured dress hats use exact EU or US sizes and generally run truer. Knit and stretch hats are made from elastic fabric and usually fit a wide range. When buying online, always check the brand-specific size chart because a US 7 from one brand may feel smaller or larger than the same label from another.
Adult hat size chart
| Circumference (cm) | Circumference (in) | EU | US | UK | Letter |
|---|---|---|---|---|---|
| 51 | 20 1/8 | 51 | 6 3/8 | 6 1/4 | XS |
| 52 | 20 1/2 | 52 | 6 1/2 | 6 3/8 | XS |
| 53 | 20 7/8 | 53 | 6 5/8 | 6 1/2 | XS |
| 54 | 21 1/4 | 54 | 6 3/4 | 6 5/8 | S |
| 55 | 21 5/8 | 55 | 6 7/8 | 6 3/4 | S |
| 56 | 22 | 56 | 7 | 6 7/8 | M |
| 57 | 22 1/2 | 57 | 7 1/8 | 7 | M |
| 58 | 22 7/8 | 58 | 7 1/4 | 7 1/8 | L |
| 59 | 23 1/4 | 59 | 7 3/8 | 7 1/4 | L |
| 60 | 23 5/8 | 60 | 7 1/2 | 7 3/8 | XL |
| 61 | 24 | 61 | 7 5/8 | 7 1/2 | XL |
| 62 | 24 1/2 | 62 | 7 3/4 | 7 5/8 | XXL |
| 63 | 24 7/8 | 63 | 7 7/8 | 7 3/4 | XXL |
| 64 | 25 1/4 | 64 | 8 | 7 7/8 | XXXL |
| 65 | 25 5/8 | 65 | 8 1/8 | 8 | XXXL |
| 66 | 26 | 66 | 8 1/4 | 8 1/8 | 4XL |
| 67 | 26 3/8 | 67 | 8 3/8 | 8 1/4 | 4XL |
Head circumference to hat size conversion for adults. When between sizes, select the next size up.
Frequently asked questions
How do I measure my head size for a hat?
Wrap a soft tape measure around the widest part of your head, about 1 cm above your ears and across the middle of your forehead. Keep the tape level all the way around and pull it snug but not tight. Read the measurement in centimetres (for EU sizing) or inches (for US/UK sizing). If your number falls between two hat sizes, choose the larger one.
What is the average hat size for adults?
The average head circumference for adult men is around 58-59 cm (about 22.8-23.2 inches), which corresponds to a US 7 1/4-7 3/8, EU 58-59, or a size Large. For adult women, the average is around 56-57 cm (US 7-7 1/8, EU 56-57), typically a Medium. These are just averages: head sizes range from about 51 cm to 67 cm in the general population.
What is the difference between US and UK hat sizes?
US and UK hat sizes look almost identical but the UK size is one-eighth of an inch smaller than the US size. For example, a US 7 1/8 hat and a UK 7 hat are typically the same physical item, just labeled differently. Both are derived from dividing head circumference in inches by pi and rounding to the nearest one-eighth of an inch.
How do I convert EU hat size to US hat size?
To convert EU to US, divide the EU size (in cm) by pi and round to the nearest eighth of an inch. For example, EU 57 divided by 3.14159 is about 18.15 inches, then multiply by 8 to get approximately 57 eighths, which is 7 1/8. Alternatively, use the size chart on this page to look up the conversion directly.
My hat feels too big. What can I do?
Use foam hat-size reducer inserts or self-adhesive hat tape on the inside sweatband. One strip typically reduces the fit by about 0.5 cm; two strips bring it down by about 1 cm. These are inexpensive and easy to apply. For structured hats, a haberdasher or hatter can also re-sweat the inner band to a smaller circumference.
Does head shape matter for hat sizing?
Yes. Most hat sizing charts assume an oval head shape (roughly 1:1.15 ratio of front-to-back depth to width). If your head is more round than average, you may find standard oval-crown hats feel snug at the front and back. If your head is longer than average (long oval), a round-oval crown may pinch at the sides. Many premium hat makers offer round oval and long oval crown options in the same size.