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.
That is a very good tip particularly to those new to the blogosphere. Brief but very accurate infoÖ Thanks for sharing this one. A must read post!
Hello there! I could have sworn Iíve visited this web site before but after going through a few of the articles I realized itís new to me. Regardless, Iím certainly happy I came across it and Iíll be book-marking it and checking back often!
Glad it was helpful
Brilliant – If you are into model railroads this can save you a ton of time.
Thanks! This was just what I needed.
R=((W×W/4)+(H×H))/2H
So I have a island that’s 111 inches long and 40″ wide at the corners and at the top of the curve I want it to be 44″. How would you draw that curve
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
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.
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
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
This worked great thanks!!!
The real questions are; how did you draw and how did you cut it?
It’s all explained in the video.
Is there an app to download it,?
No just enter the values on the web page and it calculates the radius for you.
Thanks so much! I used this and it saved me a LOT of time…. me + remembering high school math = frustration. lol’