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What is the difference between E26, E27 and A19?

Posted by Sales Team on

Shoppers of LED Light bulbs often confuse the specifications for base type (E26 or E27) and bulb shape (A19). 

Base Type

E26 E27 LED Bulb Base

Screw in bulbs use a base called an Edison Screw or ES base. This base was developed by Thomas Edison for the first light bulbs and is still in use today.

There are four commonly used thread size groups for lamps:

  1. Candelabra: E12 North America, E11 in Europe
  2. Intermediate: E17 North America, E14 (Small ES, SES) in Europe
  3. Medium or standard: E26 (MES) in North America, E27 (ES) in Europe
  4. Mogul: E39 North America, E40 (Goliath ES) in Europe.

The number following the E indicates the size in mm of the external thread screw. Thus a E26 has a 26 mm base diameter. 

You may see low cost LED bulbs using an E27 base on eBay and Amazon from foreign suppliers. While these technically will work in E26 bases, this is usually a sure indication that the bulb was not strictly designed for the US market and this bulb may lack a proper North American, UL or ETL safety certification and therefore should be avoided. 

Bulb Shape

Now that we have learned that E26 and E27 are terms used to describe the type of base used what does A19 or bulbs with an A designation mean?

A type describes a bulb that has a pear-like shape. The number that follows the "A" within the A series indicates the width of the bulb in one-eighth inch units or in millimeters.

The most commonly used A-series light bulb type is the A19 bulb which is 2 38 inches (60 mm) wide at its widest point and approximately 4 38 inches (110 mm) in length. This is the classic shape that most people are used to when shopping for a "Light Bulb". You can use this handy image below to identify the size of your A Shaped bulb:

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  • way way way back… what is a MM?

    terry grant on
  • can you put more facts about light bulbs? Please!

    janny on
  • Very clear and also very interesting that ES means the today’s bulbs are linked through nomenclature all the way back to their inventor, Thomas Edison. ES = Edison Shape. All this time . . . I never knew! Standard bulb is A19. I assume the A is for Alva, Edison’s middle name?

    That Mike Gaba guy sure doesn’t have very good reading comprehension skills. I’m glad he isn’t teaching my children.

    Mike Stirewalt on
  • Thank you for such a concise and clear explanation! I’ve redone all the lighting in my home during renovation and have been so confused online when looking for what bulbs I need and want to buy. Now, I clearly understand!

    The “Exx” is for the base type and size — I understand, Edison and size in mm. However, I want to check my thinking related to the shape of the bulb. Am I correct in thinking that for the shape of the bulb the letter “A” is used as the first letter of the alphabet because it is the most common/standard shape? In other words, “G” for globe, “T” for tube, “B” for bulged, “A” for standard…or does the “A” stand for something specific like with the other examples I provided?

    Thank you again…your simple explanation was the most helpful I have found.


    Callie on
  • Absolutely crystal clear explanation, unlike many others on the web. Thank You.

    Bill Ng on

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