Things You'll Need

Instructions

1

Measure the old door if you are replacing an existing door with one of the same size, or the new door of choice if you are building a new garage. Look at standard sizes and price your options, then note the measurements you will be using.
2

Add 18 inches to the height of the door. This is how much you need for backroom, or the space from the top of the door back towards the garage interior.
3

Add 6 to 14 inches to the height of the door for headroom, or the space directly above the closed door. Refer to the headroom requirements for the specific door you are using to see if your existing space can accommodate the new door without modification.
4

Add 7 1/2 inches to the width of the door for side room (3 3/4 inches on each side).