Arc length is the distance the clubhead travels in the backswing and through the forward swing. A short shot like a putt only needs a short arc length. A good rule for arc length is that the forward arc length should be just as long if not longer than the backswing arc length for most shots.
Coaches evan & Bradley on the arc length:
More on Swing Center:
Paul wilson on the proper size of swing with driver
Piers Ward & Andy Proudman on the amount of arc in your swing
Piers Ward & Andy Proudman on shortening your swing for consistency
