How do I find my bulb fitting?

The quickest way to identify a bulb fitting is to remove the bulb, examine its base, and compare it to common socket designs. In practice, you’ll want to know whether you have an Edison screw, bayonet, or pin-based base, and confirm the fixture’s voltage. With the base type in hand, you can confidently shop for the correct replacement.

Common bulb bases you'll encounter

Understanding the most common socket designs helps you distinguish replacements quickly. The following base types cover the vast majority of residential lighting fixtures.

• Edison screw bases — E26 (26 mm) in North America and E27 (27 mm) in Europe and many other regions; these screw into threaded sockets.


• Candelabra and small screw bases — E12 (candelabra, common in the US) and E14 (small Edison, common in Europe); both screw into smaller threads than E26/E27.


• Bayonet bases — B22d (22 mm diameter with two side pins); common in the UK, Ireland, Australia, and others.


• Twist-and-lock bases — GU10 (two pins that twist into a ceramic socket; often used for spotlights) and GU24 (two pins, older design, less common today).


• Pin bases — G4, G5.3, G9 (pin-style connectors found in various decorative and under-cabinet fixtures; note pin spacing and voltage requirements).

Interpreting base codes

Reading the base code helps you shop accurately: “E” indicates Edison screw, with the number showing the diameter in millimeters; “B” signals bayonet with a pin arrangement; “GU” or “G” denotes twist-lock or pin-based designs. Knowing these codes can save you from buying the wrong part.

With these base types in mind, you can identify most residential bulb fittings by comparing the bulb’s base to these descriptions and checking the fixture socket for clues.

Steps to determine the correct fitting in your fixture

To avoid guesswork, follow a safe, methodical process that confirms base type, voltage, and wattage before buying a replacement.

1. Turn off power at the switch or circuit breaker and allow the bulb to cool completely.


2. Carefully remove the bulb and inspect the base: screw-in (threads), bayonet (two side pins), or pin base (two or more pins).


3. Measure or compare the base diameter: roughly 26–27 mm for E26/E27; ~22 mm for B22; note any pin spacing for GU10, GU24, or G-series pins.


4. Check the fixture socket or labeling for the base type, voltage rating (e.g., 120V vs 230V), and whether a dimmer is present.


5. If the base type remains unclear, photograph the base and socket, then consult manuals, retailer listings, or bring the bulb to a lighting store for confirmation.


6. Once you’ve confirmed the base and voltage, select a replacement that matches the base and the required wattage or use a compatible LED with the same base and equivalent brightness.

Concluding paragraph: Following these steps will minimize the risk of incompatibility and ensure a safe, effective lighting replacement.

Additional considerations

Beyond base type and voltage, consider whether the fixture is dimmable and if the replacement supports it. If you’re swapping to LEDs, verify compatibility with the dimmer and fixture’s electronics, especially for track lighting or low-voltage setups.

Summary

Finding your bulb fitting boils down to identifying the base type, verifying the socket’s voltage, and matching wattage. Start by carefully removing the bulb, comparing the base to common designs (E26/E27, E12/E14, B22, GU10, GU24, G-series), and checking any fixture labels or manuals. With these checks, you’ll be able to purchase the correct bulb on the first try and keep your lighting running safely and efficiently.

How to find bulb fitting size?

Light bulb bases are identified by a code consisting of letters and numbers:

1. The first letter or letters indicate the type of base (i.e., bayonet cap or Edison screw).
2. The number indicates the diameter of the base or the distance between the pins (depending on the bulb type) in millimetres.

How do you know which bulb will fit?

To know if a bulb will fit, check the base type and size by looking at the old bulb or fixture for a code like "E26," which indicates an Edison screw base that's 26mm in diameter. Also, ensure the voltage matches your fixture, as it is dictated by the device itself, and check the maximum wattage listed on the fixture to prevent damage or overheating.
 
Check the bulb's base and shape 

• Find the code: Look on the old bulb, its packaging, or the fixture itself for a base type and size code, such as "E26" for the common Edison screw base in the US. 
• Understand the code: The letter indicates the shape (e.g., 'E' for Edison screw, 'G' for globe, 'C' for candelabra) and the number indicates the diameter in millimeters (e.g., an E12 base is 12mm). 
• Consider the shape: The bulb's shape, like A19, T, or R, also needs to be compatible with the fixture, especially for things like recessed lighting or lamp shades. 

This video explains how to identify the correct base and shape for your light bulb: 59sHunter Fan CompanyYouTube · Nov 23, 2021
Check the wattage and voltage 

• Find the wattage limit: Look on the fixture for a sticker or inscription that specifies the maximum wattage it can handle. 
• Match the wattage: You can often use a bulb with a lower wattage than the maximum, but using a higher one can be a fire hazard or damage the fixture. 
• Match the voltage: The voltage requirement is determined by the fixture. For a standard US home fixture, you will likely need a 120V bulb. 

You can watch this video to learn how to choose the right wattage for your light bulb: 1mLowe's Home ImprovementYouTube · Jan 4, 2023
Other considerations

• Dimmable: If your fixture has a dimmer switch, you will need a bulb specifically labeled as "dimmable". 
• Look for "CANbus" compatibility: If you are replacing a bulb in a vehicle, you may need a "CANbus-compatible" bulb, which has a built-in resistor. 

How do I identify my light bulb fitting?

Light bulb fitting types are usually identified with a letter followed by a number. The letter generally refers to the type of fitting, and the number is the diameter in millimetres of the bottom of the cap itself (not including any pins).

How to solve the light bulb puzzle?

Which light bulbs will be turned. On. So how can we solve this puzzle. Let's work through it logically. And go through it step by step a good starting point is just to focus on light bulb.