What it measures
Impact offset is the horizontal distance from the center of the clubface to the spot where the ball made contact, measured in millimeters or inches. The miss is labeled toe side or heel side, with toe side strikes positive and heel side strikes negative.
Because toe and heel are parts of the club, the labels mean the same thing for right and left handed golfers. Only the resulting curve direction flips with handedness.
Typical numbers
There is no tour average to chase here. The goal is a value close to zero and a tight cluster. Skilled players usually keep driver strikes within a few millimeters of center, often favoring slightly toward the toe, while higher handicap players show a wider and more random spread. Misses of 10 to 20 mm are common for everyday golfers, especially with driver.
What changes it
Your distance from the ball at impact is the main factor. Standing up or moving toward the ball in the downswing often moves contact toward the heel, while pulling away or narrowing the arms tends to move it toward the toe. Setup posture and ball position, club length and lie angle also shift it.
What it changes
Any miss away from center loses ball speed and smash factor. With drivers and fairway woods, the curved face and the head twisting at impact create gear effect. For a right handed golfer, a toe strike tends to add draw or hook spin and lower overall spin, while a heel strike tends to add fade or slice spin and raise spin. Gear effect can partly cancel or add to the curve that face to path creates, so the result is not always predictable on big misses.
Irons show much less gear effect. On irons, heel and toe misses mostly cost speed, and the face twisting can push the start direction slightly.
How to use it
Check impact offset before changing anything else in your swing. A slice that comes with heel strikes may be partly a contact problem rather than only a face problem.
In the bay, try the gate drill: place two tees or headcovers just outside the toe and heel of the club at address, leaving a little more than a ball width, and hit shots without touching them. Watch the offset numbers settle toward zero. You can also alternate deliberately hitting toe and heel to learn what each miss feels like and how the ball flight changes.