The correct way to measure the circumference of a soccer ball:
1.) Inflate ball to proper pressure.
2.) Place ball in the corner of a 90° angle. Example, place ball on a table top that butts up against a 90° wall, making sure the ball is touching both the table top and the wall. A large panel of the ball should be touching the wall and also facing away from the wall towards you.
3.) Then place a square up against a large panel of the ball, which is 180° degrees from the large panel of the ball which is touching the wall, as if you are using the square to hold the ball in place, against the wall. But do not apply any pressure against the ball, with the square, only very slight pressure, enough to hold the ball in place, without indenting the ball panel.
4.) Then mark a spot on the table top, where the front of the square is touching both the ball and table. The distance from the wall to this mark is the diameter of the ball.
5.) Now measure that distance with a CM rule, and then multiply that measurement times 3.14, and the result will be the circumference of the ball, in CM.
6.) Use a fine grade of rule, as a cheap rule with thick lines will give you poor readings. And do not use a tailors tape.