Glass Pendant Lamp Shades are available in a variety of sizes. The two most common outside diameters are two inch and three inches. Four inch outside shades are often reproductions for gas lighting reproductions. Sizes are given as fitter sizes. If you shade is broken you would be able to measure the fitter or the opening the shade site into. A 2 1/4" fitter has a two inch ouside glass diameter and a 3" outside diameter has a 2 7/8" outside glass diameter.