Tower radius circle

Hi all,I have a question about a tower defence game I'm working on,I want to set up a visual radius around my towers when there touched,say my tower has 100 range in the turret behaviour how do I know what size sprite to create to accommodate the 100 range.or must I use another technique to make that happen.

Turret properties

Range

The range, in pixels, that the turret can detect targets in. Any targets further away from the turret than this distance will be ignored.

So a circle with 200 pixel diameter centered on your turret will represent a range of 100.

Thanks for that.