What formula should I use to know how far to stand away from the ball at address.?
There is no set formula, each golfer is different. What I would recommend is starting with the club shaft at a forty-five degree angle and find out where the ball meets the club face. If the ball hits the heel of the club, you are too close to the ball, if it hits the toe of the club you are probably too far away. Another important thing is to find a way to key your distance so that you stand the same way every time. Some experts recommend grip your club with your top hand, with your club touching the ground behind the ball, and extending your fingers out to touch the same spot on your body each time as you take your stance.