Knock in a small post in the centre of the circle. Tie a string to the post, just about 4 inches above the ground. Tie the other end of the string, the length of which is the radius of the circle, to an edging tool or spade, at the bottom of the shaft. Then go around, pushing the tool into the lawn. Remove the post and dig the outside circle deeper, and remove the turf. Then hey presto you have cut out the circle.

cheers for that tips on putting circle in my lawn.

did similar with the string but tied it to an old carving knife in stead of a spade. ran that around the soil instead. perfect circle.