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Some lightbulbs only have the letter code. If this is the case, you will have to measure the bulb yourself to find the circumference. Multiply this number by 8 to find the code. For example, a 2 1/2” PAR-type lightbulb is a PAR-20. [5]

Remember, make sure to buy a bulb with the correct wattage. Otherwise, you risk starting a fire. This information can be found on the dead bulb.

There are varying socket sizes for light fixtures. To choose the correct size of bulb, look on the bottom or top of the burnt out lightbulb or around the fixture’s socket. You will see some letters that are occasionally followed by a series of numbers. This is the code for the lightbulb you will need to find at the store. Bring the dead lightbulb with you to the hardware store to find a replacement more easily.