Cutting a circular workpiece is a common woodworking challenge. There are several methods, but I found one that I come back to time and again — making it on the router table.
In order to make circles at the router table, all you need is a large plywood base. A runner on the edge of the base rides along the side of the router table to let you rout into the base with control. And a dowel on the base creates a pivot point for rotating a workpiece above it.
You can cut circles of varying diameter with this method. Just cut into the base with the router bit until the distance from the centre of the dowel to the edge of the bit matches the radius of your circle. Then clamp the base in place.
Next, cut the blank to size as shown above, and drill a hole in the centre of the blank to fit over the dowel in the base. With the blank in place, turn on the router, and rotate it counter-clockwise. A thick blank will need to be routed by raising the bit slightly between each pass.