Find the perfect lamp shade based on the height of the shade. Measure in a straight line from the outside of the top edge down to the outside of the bottom edge. This may be different from the 'vertical height' of the shade if the shade has a sloped or curved side. Another way to think of it is to measure the height on a diagonal. The slant height helps us to identify similar shades which are not always obvious based on the vertical height, depending on the different slope of the sides of the shade.