Radius Calculator (aka How to Cut a Curve in Wood)

My Radius Calculator tells you the radius of an arc of a certain width and height. You can use a string or tape measure with the radius to draw an arc on a piece of wood, or a piece of paper, or fabric, or a garden in a lawn, or a thousand other uses!

I created this calculator for my IKEA Hack Bed Bridge Bookcase when I needed to cut the arched piece at the top of each bookcase. I searched the Internet and couldn’t find a simple calculator for woodworkers to use for this purpose.

These curved arches make a huge visual design difference because the standard IKEA cabinets have very hard edges.

You could easily omit the fluted trim on the project, and it would still look elegant with the arches alone.

(For clarification, the “arc” is the curved line that I draw on the wood. The “arch” is the finished piece of wood after I cut the “arc”.)

How to use the Radius Calculator

The first step is to determine the width (W) of the arc that you want to draw. As you can see in the photo above, I sized my arc to be between the two pieces of fluted trim with 1/2″ margin on each end.

Second, you need to decide the height (H) of the arc. The height of the arc on my project was 1″.

Finally, press the Calculate and the radius (R) will be shown. Press Clear if you want to try different values.

Note: This calculator doesn’t care if you are using inches, feet, centimeters or miles! You just need to be consistent for all measurements.

10 Responses

1. Cathy says:

I’m having trouble getting a curve on a 51.5” length at 3” high. Any suggestions. It’s either too short or too long. Is there an easy way to do this alone?
Thanks

• Chris Heider says:

My calculator says you’d need a string 10-feet long to draw that arch with my method! I suggest you try this alternative method from the Samurai Carpenter instead. Let me know how that goes.

2. kamille almeida says:

Hi I just had a question I watched your video and this seems a bit dumb but the radius you got was 25.625=28 & 5/8th how did you get the 5/8 part. I am horrible at Math. Oh yeah great video by the way

• Chris Heider says:

Thanks! The radius calculator said 28.625 inches. I’ve used eighths so often that I memorized them:
1/8 = 0.125
2/8 = 1/4 = .25
3/8 = 0.375
4/8 = 1/2 = 0.5
5/8 = 0.625
6/8 = 3/4 = 0.75
7/8 = 0.875

3. TStark1218 says:

This worked great thanks!!!

4. Scott says:

The real questions are; how did you draw and how did you cut it?

• Chris Heider says:

It’s all explained in the video.

5. Jhon says: