If you ever come home from the antique market with a new lamp base sans lampshade, take heed of this golden rule before rushing out to grab any old covering. For one, lampshades come in a variety of shapes (empire, square, drum, oval) and an overwhelming range of sizes. Thankfully, the golden rule is actually an equation of measurements that will point you to the perfect lampshade to match your newfound lamp. First, measure the base and height of your lamp. The shade should be twice as wide as the lamp base, and one third of the total height of the lamp. So for a 6-inch lamp base, the shade should be at least 12 inches wide. And if the total height of the lamp (including the bulb and harp) is 24 inches, the shade should be 8 inches tall. If you prefer to follow rules with a visual aid, watch this video and never come home with the wrong lampshade again.