Choosing the right size lamp shade depends on the size and shape of your lamp. Here are some guidelines from various sources to help you choose the right size lamp shade:

• 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.
• The height of your lamp shade should be about two-thirds the height of the lamp base (give or take an inch) .
• The shade should ideally be at least one centimeter (half an inch) wider than the base on both sides to keep the whole lamp looking balanced.
• The widest part of your shade should be at least a half-inch wider than the widest part of your base on each side.
• The height of the shade should be about three-quarters the height of the base for smaller lamps like table lamps.
• Lamp shades come in various sizes, and it’s important to get the appropriate one for the lamp base. If you’re looking for a lamp shade for a table lamp, it’s best to select a shade with a height of around 2/3 the height of the lamp base. If you’re purchasing a shade for a floor lamp, you’ll want to choose one with a height of around 1/3 the height of the base.

In summary, the size of the lamp shade should be proportional to the size of the lamp base, and the height of the shade should be about two-thirds the height of the lamp base. The widest part of the shade should be at least a half-inch wider than the widest part of the base on each side. If youre still unsure, take your lamp to the store with you to try on various options to get the look and fit you want.