The most common light bulb shapes and sizes

Light bulbs are identified using a code similar to the code used for the bulb, so identifying the size of a light bulb is simple. The letters in a bulb code indicate its shape and special features such as reflector type. The numbers of the bulb indicate its size.

The most common light bulb shapes include: 

• A for Standard Household/Arbitrary 

• C for Candle 

• R for Reflector 

• MR for Multifaceted Reflector or Quartz Reflector Lamp 

• PAR for Parabolic Aluminized Reflector 

• G for Globe 

• T for Tubular 

Light bulb bases also come in a variety of sizes. They are identified by light bulb base codes, with the letter denoting the shape of the base and the number denoting the size. If you find yourself unsure of your bulb’s base compatibility, consult a store associate for advice in finding the best fit.  

The most common light bulb base sizes include:  

Standard-Medium, a regular sized screw in base: E26 or E27

Candelabra, a smaller screw in base: E12

Intermediate: E17

Bi-pin, a pin-in base with two points of contact: G4 or GU24

Twist-And-Lock base: GU10