How to measure a lampshade. There are six basic lampshade shapes: coolie, drum, empire, bell, oval and square. It is important to find out the right lampshade size. Dimensions typically given are: top x bottom x height on the vertical slant. The taller the lamp, the larger the shade. Height is the most significant factor in choosing the lampshade; in fact, it must cover the hardware but at the same time be proportionate to the base size. As well, width is the next important measurement: it is necessary to get 3-4 inches space from the bulb to the shade, especially for higher wattage bulbs. Be sure the top opening is wide enough to vent the heat.
a) vertical height; b) bottom width; c) vertical slant; d) top diameter.
The bottom size/width of the shade (b) should be similar or equal to its lamp base height (c).
The shade vertical height (a) should be about two-thirds the lamp base height/size (c).
The lower lampshade size/width (b) should be approximately one-third up to 50% wider than the widest part of its base (d).