# How are hat sizes measured?

**URL:** <https://boards.straightdope.com/t/how-are-hat-sizes-measured/195757>\
**Category:** Factual Questions\
**Created:** [August 17, 2003, 12:07pm UTC](https://boards.straightdope.com/t/how-are-hat-sizes-measured/195757 "2003-08-17T12:07:20Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\
**Post date:** [August 17, 2003, 12:07pm UTC](https://boards.straightdope.com/t/how-are-hat-sizes-measured/195757/1 "2003-08-17T12:07:20Z")

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If a particular hat says for example “7 1/8” inside the brim, what is that referring to? I thought it might be diameter, but a lot of hats are longer than they are wide, so what dimension do they use?

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**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\
**Post date:** [August 17, 2003, 12:34pm UTC](https://boards.straightdope.com/t/how-are-hat-sizes-measured/195757/2 "2003-08-17T12:34:34Z")

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IIRC, it’s the circumference of the head divided by three.

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**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\
**Post date:** [August 17, 2003, 12:52pm UTC](https://boards.straightdope.com/t/how-are-hat-sizes-measured/195757/3 "2003-08-17T12:52:52Z")

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> [@](#):
>
> \*Originally posted by Mr. Blue Sky \*  
> \*\*IIRC, it’s the circumference of the head divided by three. \*\*

When come back, bring [symbol]p[/symbol].

[Hat Sizing Scales](http://www.panamas.co.uk/info_hatsize.htm)

> [@](#):
>
> Hat size is usually generally measured in one of three different sizing scales; British, North American or European/Metric.
> 
> British hat sizes are given in an imperial measurement of the diameter of the head in inches. Sizes usually range from 6 1/2 to 8. North American hats use the imperial scale however measurements are an eighth of an inch larger than British hats for the same size hat. European hat sizes use the metric sizing standard which is a measure of head circumference given in centimeters. Metric sizes usually range from 52 - 64.

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**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\
**Post date:** [August 18, 2003, 5:18pm UTC](https://boards.straightdope.com/t/how-are-hat-sizes-measured/195757/4 "2003-08-18T17:18:17Z")

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FWIW, the size is the computationally-derived diameter of the head. As the OP notes, heads aren’t perfectly round.

If you’re making a hat, measure the head, add half an inch for comfort (most sized hats can be adjusted down in size by placing filler materal in the hatband - 1/16" thick sponge exists for just this purpose) and cut the hatband to that size. Otherwise, divide that number by pi, convert the decimal to fraction and look for that size.