【How-to】Does par30 fit par38 - Howto.org

The term A19 is used to describe the overall shape and dimensions of a light bulb. … The two digits after the letter refer to the bulb’s diameter at its widest point, and is measured in eighths of an inch. An A19 bulb, therefore, has a diameter of 19 divided by 8 inches, or approximately 2.4 inches.