Use a hack saw to cut the trim to the length you need.
Trim around garage door opening.
Measure the inside dimensions of the garage door jamb horizontally across the top and vertically along both sides.
If you are adding trim to other parts of the door cut those pieces out as well.
You will need to measure both the height and the width of the garage door.
Install head mantle piece first up tight to header level then nail in every other hole with 1 roofing nails in vinyl nailing flange.
Instructions for garage door trim.
Learn how to install our vinyl thermostop garage door trim.
Check existing rough opening for proper height width and plumb.