The belly putter is the middle tier of putters, offering more control over the head of the putter than a standard putter, which is supported by only the hands. As a result, it offers more consistency, but still allows for more touch than a full-length putter, which extends up to the golfer's chest. With the top of the putter nestled against his belly, the golfer uses his belly to anchor one end of the putter, creating a pendulum shape to his stroke.
Hold a regular-length putter in both hands, and approach the ball with your feet in your natural position when addressing a putt.
Place the putter head behind the ball, and relax your body so that you are in your most comfortable putting stance.
Use the tape measure to measure the distance from the bottom of the putter's shaft, past the end of the putter, and into your belly. The putter should contact your belly near your belly button, though the exact location can vary depending on how erect or bent over you stand when approaching a putt. A partner is required for this step.
Visit a pro shop with the measurement from Step 3, and have a belly putter shaft cut to that length and attached to the head of your putter.