Measuring for your new garage door is actually a very simple process.
Use a tape measure to measure the Garage Door’s opening from side to side near the floor of the garage. Measuring large dimensions of a Garage Door can be very tricky for one person. Ask a friend to help you hold one end of the measuring tape. Record this first measurement and all subsequent measurements on a piece of paper.
Measure the door’s opening from side to side again, this time near the topmost part of the Garage opening. Measuring both top and bottom width-wise dimensions will let you know if the door warped—if you get two differing dimensions at each point, then your door’s opening is slanted or bent, and you should hire a contractor to fix the problem.