If you are replacing a garage door the easiest way to determine the size you need is to simply measure the existing door.
How tall is the average garage door.
Recreational vehicles loom taller than the average suv and as such need extra height built into the garage and the garage door.
In the event you are adding a door to a garage without one you will need to carefully measure the width and height of the opening.
On average it should be aroudn 12 14 feet in width and 14 feet in height.
You can get a custom height for an additional cost.
For an approximately 12 x 22 detached garage or one attached to your house the most common width is 8 or 9 feet as for the height it is 7 or 8 feet however in terms of height it can go up to 12 feet to accommodate an rv.
A rv garage door widht and height depends on the type of rv you have.
Measure the backroom the distance from the garage door opening to the back wall of the garage.
A garage will need backroom that equals the door height plus 18 inches and possibly more based on the installation of an automatic garage door opener.
Buildng own garage for rv saves on storage costs.
Use a step ladder to more easily measure the ceiling height.