You must measure up accurately before getting a new garage door to ensure you buy the correct size. Ill fitting garage doors can let out heat and can pose security issues, so measuring is essential.
The main thing you need to know is the opening size, not the panel size, as the tolerance that’s allowed will depend on the manufacturer. Once you know the size of the opening, you can work out what size door you need.
Measure the width and height, measuring between the frame and from the floor to the top of the frame. If you’re having an electric door, you’ll also need to measure the space where the motor will go. If you are choosing a sectional garage door or a round the corner garage door, this will run on tracks either up into the ceiling or around the walls of the garage. You’ll need to measure these areas too, dependent on door type.