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.

Stand on a stepladder and measure the Garage Door’s opening from top to bottom. For this measurement, you can take advantage of gravity, letting the tape measure fall to the ground for easy measurement. However, you’ll still want a friend handy to hold the stepladder for safety purposes. With this lengthwise measurement and your previous width-wise measurements, you’ll know how large the opening is for vehicle and door replacement purposes. However, additional measurements are also useful.