Keep in mind that other types of locks may be better installed at the top of the door.
Interior door height from floor.
Most homeowners split the difference and install it roughly 44 inches from the floor.
Given that most contractors install the doorknob around 36 inches from the floor a deadbolt should be positioned somewhere around 42 inches to 46 inches off the floor.
Al birdseye thanked jan moyer.
That provides minimum airflow between rooms otherwise you can end up with with air balancing problems between rooms air pressure keeps doors from closing easily.
5 8 undercut is the industry standard.
Even a nine foot ceiling is better with eight foot doors and taller window or an added transom above a standard seven foot height.
The standard height of the rough opening for a door is the door height plus 2 5 8 inches.
Interior door height off floor.
Taller doors and windows or drop the ceiling.
I have never seen a door set with that big of a gap unless it was to get past floors that were not level.
Any other exterior door has a threshold height limited to 7 inches.
To fix the issue the doors need to be removed bottom of the jambs cut and reset the door.
Means of egress doors in the irc 2018 irc section r311 3 1 restricts threshold height a required exit door in residences to 1 inches from the top of the the threshold to the floor or landing on each side of the door.
The height of common doors is 6 feet 8 inches.
That is a lot of room for unlevel you have there.
The additional room allows for a 3 4 inch top jamb a shim.