The picture below shows a basic door with door knob holes drilled in it.
To measure for these door knob holes;
1. Measure up 36” from the floor; mark the 36” height on the door, on the latch edge of the door.
The next measurement you will need is the knob set back measurement!
This is the measurement from the edge of the door to the center of your door knob hole.
New locks and knobs will tell you the setback measurement, some may be adjustable.
The most common are 2 3/8” or 2 ¾” this is the length of the knobs latch piston.
2. Measure and mark the setback measurement on the door, at the same spot as the floor height.
Lines should intersect.
3. Knobs require a hole diameter of 1 7/8” to 2 1/8”. A new lock will tell you this size.
Knobs require two holes, one for a knob and one for a latch piston.
A latch piston hole must be drilled into the edge of the door, at the same height off the floor as the knob.
The knob latch piston hole’s diameter can change. A new lock will tell you this size.
Most common latch piston, sizes are 7/8”, 1”, 1 1/8”
See jamb 101 for knob latch requirements.
Do you need help?