Place the target on a grid coordinate, then press space to draw a circle of that radius. Radius is calculated in grid units with "dist to origin," and area is calculated automatically. Press the green flag again if you want to reset the grid, or just keep making circles around the origin.
The script for actually drawing the circle was cribbed from rakhi's "Draw a circle" project. All of the props! (I did change the equivalences to inequalities in order to accommodate the fact that the radius might not be an integer.)