The A19 term for light bulbs is used to describe the overall shape and dimensions of a bulb. The A19 bulbs are larger than A15 bulbs. The letters designate the bulb shape while the number represents the diameter in eight of an inch. For A19 the "A" refers to the overall shape of the bulb. A classic light bulb shape, the A19 is commonly compared to an upside-down pear. The 19 represents the bulb diameter in eight of an inch, more exactly 19/8 = 2.3 inch (or 2 3/8 inch). The length of an A19 bulb is typically 3.9 - 4.3 inches (100-110 mm) in length.