Light Bulb Dimensions

Light bulb sizes vary per country. Nevertheless, Light Bulbmost light bulbs employ letters and numbers. The letters denote the shape and the numbers the maximum diameter. The size is usually stated in millimeters or in inches.

Light Bulb Dimensions in Detail

In the United States, light bulls are measured in inches; a bulb labeled R20 is 2.5 inches. In nations that use millimeters, the bulb will be called an R63 (63 mm).

It isn’t always the case though; a PAR 38 is always called by that name whatever the region. The PAR (Parabolic Aluminized Reflector) comes in a variety of sizes. The 120V sizes are the PAR 16, 20, 30, 38, 56 and 64. The 230V sizes are the PAR 38, 56 and 64.

Fluorescent Light Bulb Sizes

The diameter of fluorescent light bulbs is determined by the tube’s diameter. The size is denoted in eights of an inch. That is, a 1 2/2 in is a T12. The most widely used bi pin size is the medium bi pin. They are available in 25, 30 and 40 watts. Lamps that measure 15 in are 14 watts and 18 in lamps are 15 watts.

Besides the T12, other types are available. The F152T8 lamp has the following specs (15 watts, T12, bi pin and is 18" long). The F20T12 lamp specs are: 20 watts, T12 bulb, bi pin and 24 in long. The F30T8 lamp bulb is T8 with 30 watts with a length of 36 in.

The light bulb size and specifications of the F30T12 lamp are the following (30 watts, T12, 36 in, bi pin), For the F32T8 lamp, it is 32 watts, T8, bi pin and 48 in. The F40T12 is the most widely used; 40 watts, T12, bi pin and 48".

The FB40/U6 specs are: 40 watts, T12, 22.5" with a bi pin base. The F40T12/ES lamp specs are 34 watts, T12, 48" with a bi pin base. For the F48T12 it is 39 watts, T12 and a single pin base. The length is 46". The F48T12/HO specs are 60 watts, T12 bulb and a RDC base. The length is 46".

Other Light Bulb Sizes

For the F72T12, the base is single pin. The length is 72. The watts are 55 and the bulb T12. The F96T12 specifications are: 75 watts, T12, 96" and a single pin base. The F96T12/ES base is single pin. The other specs are 60 watts, T12 and the length is 96". The F96T12/HO is 96" long with RDC base and with a T12 bulb.

Life Span

A 40 watt A-19 bulb has 1000 hours. A 60 watt A-19 light bulb also has 1000 hours. An A-19 bulb with 100 watts has a 750 hour lifespan. A G-25 with 25 watts has 1500 hours. A G-25 40 watt also has 1500 hours. A G-25 with 60 watts has the same life. All these light bulbs have a medium base.

Knowing something about life bulb sizes is important. It’s very likely the time will come when you’ll need to replace it. By knowing the right size, you’ll be able to get one yourself.

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Comments (2)


  1. galih says:

    Hi John,
    thanks for the input. Could you give us more info on that plz?

  2. Christina says:

    I have a lamp that needs a bulb, and I’m not sure how to calculate the dimentions of the bulb that I need. I do not have any old light bulbs to go from. Could you please provide me with the information I would need to find the dimentions?

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