Step 1: Find a 5 gallon bucket
Step 2: When plywood and math collide
You will need to find the radius for the inside bucket opening. Take your dimension and find the decimal counterpart (on a calculater 5/8 = 0.625 + 10 = 10.625). Take this dimension and divide by 2 (10.625 / 2 = 5.3125). To convert back to fractions take the decimal portion and multipy by a convenient measurement on your tape measure. My tape measure is in 1/16th, so 0.3125 x 16 = 5, or 5/16. The total radius is then 5 5/16 inches.
I used a stiff piece of cardboard and a nail to make a custom compass. Place one nail hole (where a pencil or pen will go) near the edge. Measure out your radius ( 5 5/16 inches in my example) and place another hole. Place a light nail hole the distance of the radius from each edge. This will be the center of the circle. Place the nail in the cardboard compass and use a pencil or pen to trace out the circle by using the nail as a center guide.