When I want circles I use a compass like we used in math. I have 2. You can find them usually in kits. they take up the size of an envelope and fit easily in a drawer or with you other rulers or pencils. I can make a 12" diameter circle with my compasses, the size of most large skillets. The most I paid was $7.99 for a kit that had a semi-circle eraser and the compass in it's own pouch/envelope.