If you are hanging a door on a finished floor you cut 3 4 off the bottom of the jamb then install.
Height of interior door off floor.
I like to keep 1 4 to 3 8 scribed over the finished floor.
If the door is not clearing interior flooring the better fix is often to raise the entire door jamb and threshold.
Interior door height off floor.
The standard i use is 1 2 over finish floors 3 4 is acceptable.
The height of common doors is 6 feet 8 inches.
If you are hanging a pre hung door on a bare subfloor you put the door right on the floor and install it.
Most entry door frames have a piece of lumber below the door and combined with the metal threshold will raise the base of the door off the concrete or wood sub floor by approximately 1 1 4 inches as shown in figure 2.
Cutting off the door without raising the threshold may result in an improper seal.
The standard height of the rough opening for a door is the door height plus 2 5 8 inches.
Figure 2 floor relative to entry door.
I just took a quick look at some of standards and regulations governing door undercut which is the distance between a door and finished floor as opposed to clearance which is door to sub floor.
The international building code has established doorknob height between 34 and 48 inches above a finished floor.
That is a lot of room for unlevel you have there.
Installers typically drill the hole centered 36 inches above the floor if not specifically instructed to do so differently exceptions to the rule include doors that provide egress into swimming pools or other water features.
If you decide to cut off an exterior door make sure you have a plan for sealing the bottom of the door against the threshold when the door is closed.
The additional room allows for a 3 4 inch top jamb a shim.
To fix the issue the doors need to be removed bottom of the jambs cut and reset the door.
The awi gives no minimum but a maximum of over 3 4 is unacceptable.
1 from the subfloor will usually get you in the ballpark if you dont know what the finished floor will be.
Entry doors i set a little higher if there is going to be an interior door mat.