Bulbs sizes - what is there?


Not every light bulb fits in every bulb holder. This is because bulbs have different sizes on the base, which sizes are common and standardized, and how to separate them easily is explained in detail in this post.

Validity of socket sizes

Lampholders have different sizes. These sizes are standardized and are also valid for all types and types of bulbs:

  • classic bulbs (banned since the end of 2012 and no longer available in stores
  • so-called energy-saving lamps (compact fluorescent lamps)
  • LED bulbs in pear shape

For all these types of light bulbs, the same base dimensions are used so that bulbs of different types can be screwed into a lamp socket.

Standard designation Socket dimensions - overview

designationDiameter lamp base
B1515 mm
E2727 mm
B2222 mm
E4040 mm

So you do not need to read a socket type from the lamp, if you can not find it right now, you can simply measure the socket diameter and get in this way also immediately information about which socket type it is. So you can easily see which lamp size you have to buy.

Socket for halogen lighting

Halogen lamps are not currently prohibited. A definitive ban on high-voltage halogen lighting will only be available from 2018 onwards.

Halogen lamps are not screwed in, but always plugged. Accordingly, there are different types of connectors. These are also standardized and will later be used for alternative bulbs (LED lights), since they have also been standard for a long time.

Measured here is the distance between the two plugs, which can look different to get to the numerical value.

Plug type and nameAlternative DescriptionDistance between both plug-in elements in mm
GU10none10 mm
G9GU99 mm
GU6,35GY6,356.35 mm
GU5,3none5.3 mm
GU4G44.0 mm

In addition to these particularly important and widespread dimensions, there are still a variety of special dimensions. These include, for example, measures such as

  • GZ10 (interchangeable with GU10)
  • B15d (a bayonet closure, which is rarely used in our country, but mostly only in English-speaking countries)
  • R7s (used for floor lamps, contacts are on both sides outside of the light bulb)

Tips & Tricks

The most widely used version is the E27 socket for light bulbs. It can be found almost everywhere by default and is by far the most commonly used.


Video Board: Choosing the Right Light Bulb - Step 1 The Right Fit | GE Lighting