Measureing your existing lamp shade (and determining its style) is critical in getting the best replacement match. The first step is to assess the style of the lampshade, empire, bell, coolie etc.
Lamp shades are meant to be decorative and thought should be given to the aesthetics and the look of the lamp base, not just the proportions.
For a good fit, you’ll want to measure the height of the lamp base. This will determine the diameter of the lamp shade. For example, if the base measures 14 inches in height, the shade should be 14 inches in bottom diameter.
Keep in mind that harps (the piece that shade actually connects to) come in different lengths, this can help you “fine tune” the way the shade looks on the lamp.