Next you will need to know your door height.
Pole barn garage door rough opening.
The doors extend beyond the finished trim you see from the front a fact that must be taken into consideration when framing and preparing the area for installation.
The rough opening is equal to the size of the door but you need to figure back head and side room before choosing and installing the new garage door.
The height of the rough opening would be the height of the garage door plus the thickness of whatever you are putting underneath the header in addition to the thickness of the mortar etc.
Standard garage doors in our area are 8 9 16 and 18 wide.
If you are installing a 9 wide door the opening will be 9 3 wide.
2x6 door mounting board adjusted based upon door manufacturer build make sure to leave enough turning radius for opening size and slab thickness door track radius can be between 12 and 18 depending on installation kit bracing overhead door rails in pole barn.
99 of the residential garage doors that we run across are different than these widths.