Measure a lamp's harp from the top of the harp to the bottom of the bulb socket. For the best fit, match the harp measurement with the measurement of a replacement shade.
The harp size is just one measurement to consider when replacing a lamp shade. Knowing the total height of the lamp, from the top of the harp to the lamp's base, is helpful when replacing an existing shade with one that's a different shape or size. The new shade's height should be about 40 percent of the lamp's height, according to Brown's Lampshades. However, regardless of the proportion, the shade should cover the lamp's hardware.