Now that you have considered the lamp base shape, it’s time to determine the size of the shade. Proportion is the key. Here are our guidelines for sizing a shade for a table lamp:
1) The height of the shade should be about two-thirds the height of the base. That proportion assures that the lamp won’t look top or bottom heavy.
2) The width of the shade base should be roughly equal to the height of the lamp from base to fitting. Alternately, the base of the shade should be roughly twice the the size of the widest part of the base. If you’re debating between two sizes, it’s usually better to go for the larger (although having said that, very thin and tall lamps can often be well-suited to smaller shades).
3) Floor lamps will generally take a shade with a base diameter of 16 inches or larger. Similar rules apply as for table lamp shades, where the shade needs to be tall enough to cover the hardware so that you don't see the lamp socket or fitter from the side. Also consider that because a floor lamp is much taller, it will tend to look better with a lampshade that has less of a slope to the sides, either a drum shade or something similar. The shade also will generally be larger than that of a table lamp to keep in proportion to the base.
4) Chandelier or wall sconce shades are typically much smaller than regular shades, usually in the range of 4 to 8 inches across the bottom. You'll need to make sure there is some room around the light bulb to allow for heat to flow out of the shade without presenting a safety hazard. Mini shades are specifically designed for this use. Most are designed to clip directly onto the outside of a light bulb, since the mini chandelier lampshades are relatively light weight.
SIZING THE SHADE
Proportion is the key. We recommend the height of the shade be two-thirds the height of the base and that the width of the shade base be roughly equal to the height of the base or twice the size of the widest part of the base.