Never one good with a level, two by fours, and hanging, I consider myself successful if a picture is not noticeably crooked. But if you wanted to do it perfectly, the experts have figured out the science behind hanging pictures:
The rule of thumb is to hang your picture at anywhere between 56” and 60” on center. For 57 inches, "on center” means that the middle of the picture is always 57” from the floor.
Measuring from the floor, mark 57” on the wall. Measure the height of your picture and divide by two. This is your center. Measure the top of your picture to its tightened wire, tw.
Subtract tw from ½ the picture’s height. This number will tell you how far above your initial 57” mark you should place your hook.
Example: A 20” tall photo with a tight wire located 2” below
the top should have a hook placed at 8” above the mark. 10” – 2” = 8”; the hook should be placed 65” off the floor.