Measure the height of the door with the tape measure. Write down the exact height.
Measure the exact width of the door and write this figure down.
Open the door to expose the hinges. Measure the distance between each hinge and the distance from the hinges to the edges of the door.
Remove the doorknob with the screwdriver.
Measure the distance from the top and bottom of the doorknob cutout to the edges of the door.
Replace the doorknob using the screwdriver.