Usually the professionals measure up to 36 inches from the bottom where the lock they set.
How to fit a mortice lock to a door.
On doors with a horizontal mid rail the lock should be positioned clear of the mid rail joints otherwise the joints will be weakened the lock should be fitted in the centre of the rail to clear the upper and lower joints.
Carefully remove the timber inside the lines using the same technique as for the door latch.
Remove the keep and drill a 16mm hole about 10mm deep.
To avoid any error you should mark the position where you want to install the lock on the door.
Place the body of the mortice lock against the side of the door and mark the top and bottom edges of the main body on the side of the door.
Please put a mark for keyholes strike plate and latch on the side of the door.
Fit the lock into the door and secure using screws.
Push the keep on and mark a pencil line all the way round the hole inside for the latch.
Taking and using measurements 1.
Using your measurement mark out both the top and bottom of the latch.
The correct positioning of the lock is crucial.
Use the 10mm chisel to square the hole up cutting at the top and bottom first.
This will be your guide when.
Fit the lock and check the positions of the door handle spindle and key hole adjust these if necessary.
As a guide the height of your lock should be about 1 metre high.
Trade expert michael demonstrates how to quickly fit a 5 lever security mortise 5 lever mortise lock and handles in this easy diy video by studhawk.