How to Measure a Lamp Shade
The right lamp shade not only softens the light from the lamp, but adds a decorative touch to your room. If you want to replace the shade to give your lamp a new look, it's important to know the proper measurements. Fortunately, measuring a shade is an easy process once you know exactly which parts you need to pay attention to. Nearly all shades are sized according to the top diameter, bottom diameter, and slope, so once you know the right numbers, you can easily find a new shade.
Part 1Getting the Top Measurement
You’ll have a much easier time measuring the shade if the lamp isn’t in the way. Carefully remove the shade from the lamp and set in on a table for the moment.
If the lamp has a clip-on lamp shade fitter, you can simply pull it off the light bulb. Be gentle, though, to avoid damaging the bulb. If the lamp has a spider lamp fitter with a lamp harp, unscrew the finial that holds the shade onto the harp and then lift the shade off. If your lamp has an UNO lamp shade fitter, unscrew the bulb and carefully lift the shade off.
Hold your tape measure at one end of the top edge of the lamp shade, and pull it across to the opposite edge in the right in the middle. If your shade has a square shape, measure one side of the square from corner to corner for the proper measurement.
Have a piece of paper handy to jot down the first measurement. Mark it as the “top diameter” so you know exactly what size replacement shade you need.
Part 2Recording the Side and Bottom Measurements
Once you’ve recorded the measurement for the top diameter, place the tape measure at one end of the bottom edge of the lamp shade. Pull it across to the opposite side to get the proper measurement.
Write down the second measurement with the top diameter to make sure you know the precise size of the shade. Mark this measurement as “bottom diameter.” 
Set the shade down on the table once more. Place the end of the measuring tape at the top edge of the shade, and pull it down to the bottom edge to measure the slope.
Sometimes, a shade’s slope is referred to as its height. If you have a square lamp shade, it obviously won’t have slope. Measure from top to bottom in the same manner, though, to get the height of the shade.
Record the next measurement with the top and bottom diameters. Mark it as the shade’s “slope” or “side.”
Once you’ve recorded all 3 measurements for the shade, you can choose the proper size for a new shade. Most shades list the measurements in the following order: top diameter, bottom diameter, and slope/height.
Part 3Choosing a Lamp Shade Size
It’s important to choose a shade that offers the right proportions for the lamp body or base. Opting for one that’s two-thirds the height of the body gives the lamp an attractive, balanced look.
Your lamp will have a more balanced look if the top of the shade is as wide as the bottom of the base. It also helps to choose a shade that’s the same shape as the base for a cohesive look.
Place the tape measure across the center of the lamp base from one side to the other just as you did with the shade to get the proper diameter.
You don’t want to slim down too much with the shade, so it helps if its bottom is wider than the lamp’s base, which is usually its widest part. It can help give the lamp a more dramatic look so it’s sure to stand out.