You've probably seen one, that odd-seeming door that clearly shows someone had no idea where to place the knob. Typically, the knob is higher than normal and gives you a feeling of being an awkward child as you reach up to twist it. The main concern with doorknob placement, in most of today's doors, is aesthetic. While there is something to be said for consistency, it really has no affect on the operation of the knob.
The standard height for doorknobs on a typical 80-inch tall, household door is 36 inches. Why this is standard is not certain. The most likely explanation is that, as we began to mass produce doors, the centre of most middle rails in the typical drop panelled door was 36 inches from the bottom of the door. This is how it is still measured today, with the tape measure hooked under the corner of the door to a height 36 inches up.
Backset and Boring
While the 36-inch height is the centre line for standard doorknobs, it is not the only consideration. The backset, or spacing from the edge of the door, is crucial to the operation of the knob. This measurement varies, with most mass-produced knobs being adjustable from a backset of 2 and 1/8 inches to 2 and 3/4 inches, which are the two most common backsets. Knob holes are usually 2 and 1/4 inches in diameter with the edge bore for the striker being 1 inch in diameter.
While deadbolt locks can be installed at any height along the door's edge, they are typically placed with their centre 6 inches above the centre of the knob. This gives enough space for the lock mechanism to function without bumping your wrist into the knob while still being low enough to be easily within reach. Deadbolts are normally installed with the same backset as the knob, with a similar bore diameter.
When placing a new door in an old jamb, consideration should be given to the placement of the striker plate on the knob side jamb. This plate must be lined up with the centre of the knob for proper operation of the latch. You will need to either match the height of the new knob with the existing striker plate or bore a new hole and move the plate to match the new knob. The same is true of the deadbolt receiver.
Taller doors, especially at front entrances, are becoming more common. For doors that are more than an inch or two taller or shorter than 80 inches, some adjustment is probably best. If the door has a centre rail, centring the knob in it, height wise, will work fine. If it does not have a centre rail, use your best judgement and set the knob where it is easiest and most aesthetically pleasing.