Bulb Size Reference Guide - How to Measure a Light Bulb

Bulb size is typically represented by a code that consists of a letter or letters followed by a number. The letter(s) in the code indicate the shape of the bulb, while the number relates to the diameter of the bulb in eighths of an inch.

For example, let's consider the A-19 bulb:

  • The letter "A" indicates the shape of the bulb.
  • The number "19" represents the diameter of the bulb in eighths of an inch.

To determine the actual diameter in inches, you divide the number by 8, since each number in the code corresponds to eighths of an inch. So, for the A-19 bulb:

Diameter = 19 / 8 ​= 2.375 inches

Therefore, the A-19 bulb has a diameter of 2.375 inches. This type of coding system helps consumers easily identify the size and shape of bulbs for their specific lighting needs.

Print the image below on a full page to help with understanding your bulb size

Bulb Printout