How do I find the diameter of a hole?

Hi… This is probably a stupid question, but not something I have been able to work out.

Say you have a circle or a hole in a random plane… And you want to know its diameter, how can you accuratly measure it?

The only way I can find is to click on one side of the circle/hole… Move the mouse to the other side, zoom right in… And then move along the edge of the circle until I can see the biggest value… But this can’t be the scientific way to do it?

I assumed there would be a way to “snap” to the opposite side… Or through the centre… But I can’t work it out.

Could someone help?


Activate your line tool. Hover around where you think the center should be and shortly the cursor will snap to the center point. Draw a line from the center to one of the points on the circle segments and you will get the radius.

If the hole is still a circle, meaning it hasn’t be exploded or cut in some way, the radius will be given in the Entity Info window.

if the arc/circle has been exploded (which can happen for reasons other than a user deliberately exploding it) , your method is basically the method… there are a few plugins which can help though.

they’re basically the same but the selection process is different… CLF requires the polyline to be exploded into individual segments then you select two adjacent segments as input… thomthom’s will let you select a non-arc/circle polyline as input (iirc)

A bit more color to Box’s suggestion (which I think is the best way to do this, unless your hole/circle has been exploded, as Jeff commented below):

Use the select tool to select only the perimeter of your circle, then select Window > Entity Info. The dialogue box that pops up will display the radius of the circle (and also the number of segments).

Use the dimension tool. You need to activate the large tool set to see this (view > toolbars…).
Select the dimension tool and then click on the perimeter of the circle, it will show diameter (DIA)