How to find the center of a circle

This is simply a method to find the center of a circle, using very simple techniques. You'll need a ruler, a pencil and some way of measuring right angles.

You might want to use this technique to know where to drill the hole in the middle or draw concentric circles on the surface.

I can't take any credit for this as I probably learnt it at school, many eons ago. I just thought I'd add it because I saw lots of methods for drawing circles, using bits of string, wooden battens etc. but nothing for reverse engineering the problem.

If it's not correct then I can only blame my very poor memory.

Step 1: Draw a chord across the circle

Draw a line across the circle near the edge so it cuts the circumference in two places. This is called a chord.

If you can also make the chord a nice easy length i.e. 10, 20, 24, etc this might make life easier in the next step.

Comments

[admin]

This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you have so that we can publish your work. Thanks!

[snowfalcon1]

a simpler method involves inscribing a right angle into the circle. the hypotenuse is a diameter, and then find the halfway point of the hypotenuse for the center

[deepcut71]

Or do it this way :

1. Draw a square around the circle.
2. Draw a line from top-left to bottom-right corner of square.
3. Draw a line from top-right to bottom-left corner of square.
4. Where the lines cross is the center.

[Jbouquet12]

I just got the biggest kick out of this it works perfecto.

[xAxrules]

Using this for locating pots in a project box!

[iminthebathroom]

your instructable is being applied as we speak, thanks ! ! !

[KLUTZYengineer]

In the first step, the line that you proposed was a chord, is technically a "secant", not a "chord".

[bunglesmate]

okey dokey. thanks for the technical correction.

[clicclic]

Thank you so much for this helpful technique. I wish I was smart enough to figure this out on my own; I've been stressing about perfectly centered holes on a number of recent projects and didn't know how to find the center. Thanks again - a huge help! clicclic

[bunglesmate]

Thanks for the comments. I can't take credit for this though, as I'm sure it was drummed into my skull at school. I do try to think of things some people know as being so obvious they assume everybody must know it.

[buteman]

Well you put it here and it is something many will want to do.
I am starting a project in which I will need the centers of some circles.
I was going to do what you have done as part of my own instructable but now I will just give a link to this.
Thanks

[awsome]

fairly simple...=)

[Shut Up Now]

its so simple once you know it! thanks for sharing!

[amakerguy]

that is a cool way of finding the center.

[bunglesmate]

thank you very much for your comment.

[walterr]

A clear Instructable. If you use a tangent instead of a chord you automatically have the point from where to draw the perpendicular.