Standard Door Knob Height – Most doors already have a knob hole when they are purchased. But if you buy a slab or blank door, a hole is required. Slabs or blank doors are more affordable than doors ready to hang. And you have to choose the finish and the hardware. Measuring, drilling and installing a doorknob are something that a homeowner can do DIY.
The International Building Code has established door knob height between 34 and 48 inches above a finished floor. Installers typically drill the centered hole 36 inches above the floor. If it is not expressly stated to do it differently. Exceptions to the rule include doors that provide exit in swimming pools or other sources of water. In this case, the doorknob is installed 48 to 54 inches above the floor, specifically to raise the knob out of the reach of small children.
Standard slab doors for interior are 80 inches high. But for doors that are more than one inch or two more or less than 80 inches, some adjustments door knob height are probably better. If the door has a center rail, centering the button on it, height wise, will work fine. If you do not have a center lane, use your best judgment and adjust the knob which is easier and more aesthetically pleasing.