Measure the cabinet door opening with a tape measure. Measure the opening at the top and the bottom. Take the smaller of the two measurements as the door opening width if there is a small difference in measurement.
Take the width measurement of the cabinet door with the tape measure. Once again, measure at the top and bottom of the cabinet door and take the smaller of the two measurements as the door width.
Subtract the cabinet opening measurement from the door width measurement. Once you subtract, divide the difference in half. This is your offset or overlay measurement for your hinges. For example, if you have a 1 inch difference between the opening and the door, your offset would be 1/2 inch.