2. The distance from the heel to the toe of the clubhead is not greater than 5 inches (127mm); and

3. The distance from the sole to the crown of the clubhead is not greater than 2.8 inches (71.12mm).

The way to think about this is the maximum size a golf club can be would be if you were to imagine a solid block with the dimensions 5 inches (12.7cm) long by 5 inches (12.7cm) wide by 2.8 inches (7.112cm) tall. If we were to place this solid block in a beaker, it would displace 70 cubic inches or 1147 cubic centimeters or 2.5 times the amount of the maximum sized driver!

If you closely examine a clubhead, you will notice all the angles, contours and rounded corners. These in effect limit the volume as illustrated below.