# Wood working ( math)

**URL:** <https://boards.straightdope.com/t/wood-working-math/1012200>\
**Category:** Factual Questions\
**Tags:** tools-electric-diy, science-math\
**Created:** [December 26, 2024, 8:30pm UTC](https://boards.straightdope.com/t/wood-working-math/1012200 "2024-12-26T20:30:50Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\
**Post date:** [December 26, 2024, 8:30pm UTC](https://boards.straightdope.com/t/wood-working-math/1012200/1 "2024-12-26T20:30:50Z")

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I am making a small barrel out of 1X4’s. 11.5 diameter. I am dividing the circumference by 12=3.013 inches for each board cut on 15 degrees. When I am finished the 12 points will be about 1/8" higher than the flat spot on each board. Will my 11.5 inches be on the high spot or the low spot? I plan to actually cut it slightly oversize anyway and then sand it down but the closer I can get the better.

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**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\
**Post date:** [December 26, 2024, 9:40pm UTC](https://boards.straightdope.com/t/wood-working-math/1012200/2 "2024-12-26T21:40:43Z")

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Do you want the interior diameter or the exterior diameter to be 11.5?

What you’ve calculated is the arc length of 1/12 of a 11.5 diameter circle, which isn’t quite what you want in either case.

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**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\
**Post date:** [December 26, 2024, 9:56pm UTC](https://boards.straightdope.com/t/wood-working-math/1012200/3 "2024-12-26T21:56:13Z")

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For just about any regular geometric shape like a dodecagon you can search on “dodecagon formula” and bring up your choice of websites providing helpful info like this [dodecagon calculator](https://www.omnicalculator.com/math/dodecagon) and others l[ike this one containing the formulas](https://mathmonks.com/dodecagon). One of them probably includes formulas for inscribed and circumscribed circles in a dodecagon.

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**Author:** ![HoneyBadgerDC](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/honeybadgerdc/32/1033_2.png) [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)\
**Post date:** [December 27, 2024, 1:34am UTC](https://boards.straightdope.com/t/wood-working-math/1012200/4 "2024-12-27T01:34:59Z")

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Those calculators are cool. I ended up just measuring it with a ruler and compass.