Over the years, hundreds of bulb shapes have been introduced for general and specialized applications. As needs evolve, some shapes are discontinued and others expanded. Here are some of the most common shapes used today. Each comes in a variety of sizes, wattages, colors, finishes and bases. Not all possible combinations of shape, size, wattage, color, finish and base may be available.
In America, the size of a bulb is measured in 1/8 inch increments. For example, the common A19 bulb shown below is 19/8 of an inch, or a nominal 2.375 inches in diameter. The actual diameter of an A19 bulb may slightly differ from one manufacturer to another.
The length of a specific bulb, A19 for example, is not determined by the A19 designation and is likely to be slightly different from one manufacturer to another.