Quick answer: Measure around your head just above your ears and eyebrows. Divide the inches by 3.14 to get your US hat size (or use the calculator below). A 23-inch head is a 7⅜; a 24-inch head is a 7⅝; a 25-inch head is a size 8. Anything 7½ or larger is above average and is where "one size fits most" hats stop fitting.
Hat size calculator
Enter your head measurement and we'll convert it.
Tip: use a soft tape or a piece of string, keep it level, and don't pull it tight. If you land between two sizes, size up for a fitted hat.
Hat size conversion chart
| Inches | cm | US fitted size | Letter size | Fits MONGO? |
|---|---|---|---|---|
| 21⅛ | 54 | 6¾ | S | No |
| 21½ | 55 | 6⅞ | S | No |
| 22 | 56 | 7 | M | No |
| 22⅜ | 57 | 7⅛ | M | No |
| 22¾ | 58 | 7¼ | L | No |
| 23⅛ | 59 | 7⅜ | L | Loose |
| 23⅝ | 60 | 7½ | XL | Yes |
| 24 | 61 | 7⅝ | XL | Yes |
| 24⅜ | 62 | 7¾ | XL | Yes |
| 24¾ | 63 | 7⅞ | XXL | Yes |
| 25⅛ | 64 | 8 | XXL | Yes |
| 25½ | 65 | 8⅛ | XXL | Yes |
| 26 | 66 | 8¼ | 3XL | Yes |
| 26⅜ | 67 | 8⅜ | 3XL | Yes |
| 26¾ | 68 | 8½ | 3XL | Yes |
| 27⅛ | 69 | 8⅝ | 4XL | Too small |
Letter sizes vary by brand; the column above follows the most common US convention (S 6¾–6⅞, M 7–7⅛, L 7¼–7⅜, XL 7½–7¾, XXL 7⅞–8⅛). Inch values are rounded to the nearest eighth.
How to measure your head for a hat
- Use a soft measuring tape, or a piece of string you can lay against a ruler afterward.
- Wrap it around your head about ½ inch (1 cm) above your ears and across the middle of your forehead, where a hat band sits.
- Keep the tape level and snug but not tight. Don't pull it in.
- Read the number, measure once more, and use the larger of the two.
No tape and no string? A phone charging cable works: wrap it, pinch the overlap, then measure the cable against a ruler. If you still can't measure, hat size correlates with height, so a man over 6'2" is more likely than not to be 7⅝ or above, but it's a guess.
How hat sizes work
A US fitted hat size is simply your head circumference in inches divided by pi (3.14). A 22-inch head is a size 7; a 25⅛-inch head is a size 8. UK sizes run ⅛ smaller than US, and European sizes are just the circumference in centimeters. "One size fits most" and adjustable caps are usually built for 7 to 7⅝ (22–24 inches), which is why they stop fitting right around the point where a head becomes bigger than average. The average adult man is about 7⅛ to 7¼ (22½ inches / 57 cm); anything 7½ and up is above average.
What if you're 7½ or bigger?
That's the range MONGO is built for. Every MONGO hat fits 7½ through 8½ (23⅝–26¾ inches / 60–68 cm) with a deeper crown, so it sits down on your head instead of perching on top, and an extended-range snapback that closes with notches to spare. If it doesn't fit, return shipping is on us.
Shop hats built for sizes 7½–8½
Free US ground shipping. 30-day fit guarantee: if it doesn't fit, return shipping is on us.
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Quick answers
What hat size is 23 inches?
23 inches is a US size 7⅜ (about 58.5 cm), letter size L. Standard adjustable hats fit; MONGO will feel slightly loose.
What hat size is 24 inches?
24 inches is a 7⅝ (61 cm), XL. This is the top of most "one size" ranges and squarely inside MONGO's 7½–8½ range.
What hat size is 25 inches?
25 inches is a size 8 (63.5 cm), XXL. Almost no standard hat is made in this size; MONGO fits it with room to spare.
What hat size is 22 inches?
22 inches is a size 7 (56 cm), M. Most one-size hats fit.
Is 7¼ hat size small, medium or large?
7¼ (22¾ inches / 58 cm) is a large in most US brands, though a few call it a medium. It's right around the average adult male head.
What is the average hat size?
About 7⅛–7¼ for men (22½ in / 57 cm) and 7 for women (21¾ in / 55 cm).
What's the biggest hat size?
Mainstream fitted lines usually stop at 8. Big-head brands go further; MONGO fits through 8½ (26¾ in / 68 cm).