How to Choose the Right Bulb Shapes and Sizes?

Acknowledging the bulb’s shape, size, and base is important for understanding what style is suitable for what place.

Every light bulb features identifying characteristics called light bulb codes and they are represented in the form of numbers, letters, or series of letters.

Numbers are used for indicating the size of the bulb in millimeters or 1/8 of an inch. While the letter or series of letters represent the shape or unique properties of the bulb. Using the codes, you can easily identify whether the bulb is suitable for your fixture or not.

In this article, we will take a close look at these codes and discuss the various properties of a bulb.

What Are the Different Bulb Shapes and Shape Codes?

The different bulb shapes and shape codes are as follow:

  • Arbitrary (A) Bulb shape
  • Bullet or Blunt Tip (B) Bulb shape
  • Bulged Reflector (BR) Bulb shape
  • Conical Or Candle (C) Bulb shape
  • E – Ellipsoidal bulb shape
  • F – Flame style candelabra bulb shape
  • Globe (G) Bulb shape
  • MB – Halogen Bulb shape
  • Multifaceted Reflector (MR) Bulb shape
  • Parabolic Aluminized Reflector (PAR) Bulb shape
  • P – Pear bulb shape
  • Tabular (T) Bulb shape

You can also check the below chart to see more bulb shapes:

bulb shape code

What Are the Bulb Shapes and Sizes?

Although there are a variety of bulbs sizes, we have discussed below only the ones that are most commonly used in our household or for outdoor purposes.

1. A Group:

A shaped light bulbs

A group, Arbitrary group, or Standard group bulbs are used universally for home lighting. These classically shaped bulbs are in every household, and probably we have grown up with them.

Such groups are versatile and suitable for a range of applications which include kitchen lights, ceiling lights, closet lights, lamps, vanity lights, bathrooms, etc.

Bulb’s diameter is represented in 1/8 of an inch using numbers in each code. They are the following:

Code Name Diameter In Eighth Scale
A15 bulb 15/8 = 1-7/8
A19 bulb: 19/8 = 2-3/8
A21 bulb: 21/8 = 2-5/8
A25 bulb: 25/8 = 3-1/8

For the A group bulbs, E26/E27 medium screw bases are commonly used.

2. B and C Group:

light bulbs types and sizes

Most bulbs in this category are of candle flame shape and they are also known as candle bulbs.

Blunt-Tip (B) bulbs have a bullet shape. While Conical (C) bulbs are very similar to B bulbs, however, they have a more cone-like shape.

Besides, there is another type known as Conical angular (CA) and it also has a cone shape but with a bent tip.

Such bulb types are mostly used in decorative home lighting applications like chandeliers, night lights, holiday light strands, pendant lights, decorative light strands, wall sconces, etc.

Code Name Diameter In Eighth Scale
B10 bulb 10/8 = 1-1/4
CA10 bulb 10/8 = 1-1/4
C7 bulb 7/8 = 7/8
C9 bulb  9/8 = 1-1/8
C15 bulb 15/8 = 1-7/8

For the B and C group bulbs, E12 candelabra, E17, and E26/E27 medium screw bases are commonly used.

3. BR Group:

Bulged Reflector Bulbs

Bulged Reflector (BR) bulbs have a coating of reflector material that is used to accumulate and radiate a wide beam of light off from the bulb. This is how traditional BR bulbs used to work.

However, LED BR bulbs do not need any reflector yet they can incorporate clear,  frosted, and patterned lenses with a dome shape.

It enables the light to diffuse and gradually fade into areas where light is not reaching. Such bulbs are commonly used in recessed fixtures, can fixtures, track fixtures, and display fixtures.

Code Name Diameter In Eighth Scale
BR20/R20 bulb  20/8 = 2-1/2
BR30 bulb 30/8 = 3-3/4
BR40 bulb 40/8 = 5

For the BR group bulbs, E26/E27 medium screw bases are commonly used.

4. G Group:

Globe bulbs

Globe (G) bulbs are also commonly used in households. The bulbs have a round shape and come in several sizes.

Such bulbs are suitable for use in large light fixtures such as chandeliers, foyer lights, and ornamental fixtures.

Code Name Diameter In Eighth Scale
G11 bulb 11/8 = 1-3/8
G14 bulb 14/8 = 1-3/4
G16/G50 bulb 16/8 = 2
G60 bulb 60 millimeters =2-3/8
G25/G80 bulb 80 millimeters = 3-9/64
G30 bulb 30/8 = 3-3/4

For the G group bulbs, an E26/E27 medium screw, and E12 candelabra bases are commonly used.

5. PAR Group:

Parabolic Aluminized Reflector bulbs

Traditionally, Parabolic Aluminized Reflector (PAR) incandescent bulbs come with U-shaped reflectors.

It is utilized for maximizing sharpness and navigating light in a narrow sport beam or wide flood-pattern beam via front of the bulb.

Besides, LED PAR bulbs do not incorporate reflectors, yet emit hard-edged lighting. They are smaller in size than BR bulbs and are most commonly used in floodlight fixtures, sport lights, emergency lights.

Moreover, they are also suitable for indoor use in recessed fixtures, can lights, track lights, and display fixtures.

Code Name Diameter In Eighth Scale
PAR16 bulb 16/8 = 2
PAR20 bulb 20/8 = 2-1/2
PAR30 bulb  30/8 = 3-3/4
PAR36/AR111 bulb 36/8 = 4-1/2
PAR38 bulb 38/8 = 4-3/4

For the PR group bulbs, an E26/E27 medium screw and G53 screw pin bases are commonly used.

6. MR Group:

Multifaceted Reflector Bulbs

MR stands for Multifaceted Reflector. These bulbs come with a reflective and faceted interior and are small in size.

MR LED bulbs do not need facets, however, they still often include them.

MR bulbs are suitable for a number of applications which include recessed fixtures, desk lights, track fixtures, and display case fixtures.

MR bulbs are ideal for outdoor use as well due to their low-voltage wiring systems.

Code Name Diameter In Eighth Scale
MR11 bulb 11/8 = 1-3/8
MR16 bulb  16/8 = 2

MR bulbs use completely different bases than other bulbs. For these types of bulbs GX5.3 bi-pin and GZ4 bi-pin in low-voltage AC/DC systems, and GU10 bi-pin – in 120-volt systems are used.

7. T Group:

Tabular bulbs

Tabular (T) bulbs are available in different sizes and shapes.

These types of bulbs are suitable for various applications depending on their size. These applications include pendant lights, chandelier fixtures, and garage troffer lights.

Code Name Diameter In Eighth Scale
T7 bulb 7/8 = 7/8
T8 bulb 8/8 = 1
T10 bulb 10/8 = 1-1/4
T14 bulb 14/8 = 1-3/4

T group bulbs use many different type of bases which include E26/E27 medium screw, E12 candelabra, E17, BA15D bayonet, G13 bi-pin.

What Is Your Bulb Base?

Currently, bulbs are available with 6 different types of bases. They are the following:

  • Screw bases
  • Bi-Pin bases
  • Specialty bases
  • Fluorescent pin bases
  • Twist and lock bases
  • Compact Fluorescent lamp plug-in Bases

light bulb base

 Among these, only Screw and Bi-pin bases are the two main and commonly used ones. Let’s discuss both of these in detail:

1. Screw Bases:

The most common light bulb base is a screw base. Edison base light bulbs are another name for these bulbs.

Two contact wires connect the filament to the base of an incandescent or halogen screw base light bulb, where the electrical voltage is applied. Screw bases come in a variety of sizes, and they’re labeled with a descriptive name and size on the box.

The number in the light bulb base denotes its diameter in mm. For example: if it is written E-5, then the bulb has a diameter of 5 millimeters.

Here are the most common sizes of screw base E5, E10, E11, E12, E14, E17, E26, E27, E39, E40.

2. Bi-Pin Bases

MR16s, Linear fluorescents, plug-in compact fluorescent bulbs, and a few types of HID light bulbs all have pin bases. Pin base bulbs operate on a different concept than screw base bulbs.

Pin base light fixtures have two pins that stick out of the base and link the bulb to the current, however, screw base light bulbs have two contact wires linked to the metal base and link the bulb to the current.

Electrical current can then travel via the pins and into the light bulb, activating the filament and emit light.


1. Does Light Bulb Shape Matter?

Yes, light bulb shape does matter. Hence, you can look at the above chart to identify all the bulb shapes and be mindful when purchasing a new bulb.

2. What Is the Standard Light Bulb Size?

E26 is the standard size for a light bulb in North America and E27 in Europe.


As you can see there are a variety of bulb shapes and sizes. With this article, we aimed to educate on that.

Not many people are aware that bulbs can be of so many different styles. Hopefully, this article was helpful to you and you get to learn something new from it.