What Size Light Bulb Can I Use?

Choosing the right light bulb size for your lighting needs can seem complicated, with all the different types, shapes, bases, and wattages available today. However, if you understand a few basics about light bulbs and sockets, you can easily determine what size bulb you need for any lamp or fixture in your home.

How Light Bulb Sizes Are Measured

Light bulb sizes are measured in terms of their diameter and shape. Here are some of the most common sizes:

  • A15: The standard light bulb shape, with a diameter of 2.25 inches. Also known as an E26 base incandescent bulb.
  • BR30: A bulged reflector bulb, with a diameter of 3 inches. Fits BR30 fixtures.
  • PAR30: A parabolic aluminized reflector bulb, with a diameter of 3 inches. Used in recessed and track lighting.
  • MR16: A multifaceted reflector bulb with a diameter of 2 inches. Fits MR16 fixtures.
  • T4: A tubular bulb with a diameter of 4/8 inches. Used in tube fixtures.
  • G25: A globe bulb with a diameter of 2.5 inches. Used in globe fixtures.

So if you see a label such as PAR30 or BR40, the number refers to the diameter in eighths of an inch.

Choosing the Right Base

In addition to size, you also need a bulb with the proper base to fit the lamp socket. Here are some of the most common:

  • E26/E27: The standard medium screw base used in most household lamps. Fits A15 bulbs.
  • GU24: A two pin base often used in CFLs and LEDs.
  • GU10: A small bi-pin base used in track lighting. Fits MR16 bulbs.
  • G4: A small bi-pin base used in decorative fixtures. Fits T4 bulbs.
  • E12: A smaller candelabra screw base used in chandeliers and sconces.

So always match the base of the new bulb to the socket, even if the shape and size are different. An A15 E26 bulb will not fit in a GU24 socket, for example.

Choosing the Right Shape

In addition to base and diameter, bulb shape affects what fixtures it can be used in. Here are some of the most common shapes:

  • A15: The standard pear shape used in table lamps andceiling fixtures. Provides omni-directional light.
  • BR: Bulged reflector bulbs concentrate light downward. Good for recessed cans.
  • PAR: Parabolic aluminized reflector bulbs focus light in one direction. Used in track lighting and floodlights.
  • MR: Multifaceted reflector bulbs provide more directed spot lighting. Used in track fixtures and pendants.
  • G: Globe bulbs provide decorative, omni-directional lighting. Used in globe fixtures and vanity lighting.
  • T: Tubular linear bulbs fit in tube fixtures and fluorescent fixtures.

So opt for an A15 or G shape for table lamps, a BR or PAR in recessed cans, and MR16 for track lighting. The shape helps direct the light where you need it.

Choosing the Right Wattage

Finally, consider the wattage or lumens. Higher wattage bulbs produce more light but also consume more energy. The wattage needed depends on the fixture:

  • 15-100W: Good for table lamps, ceiling fixtures, and chandeliers. Provides ambient lighting.
  • 50-150W: Best for recessed cans used as downlighting or task lighting.
  • 35-50W: Good wattage range for bathroom vanities and track heads. Provides accent lighting.
  • 25W or less: Good for smaller accent lamps and sconces. Provides mood lighting.

As a rule of thumb, choose lower wattages for ambient mood lighting and small fixtures, and higher wattages for task lighting and large spaces. Keep in mind newer LED bulbs provide the same brightness at lower wattages, so you may need to adjust down.

What Size Bulb for Common Fixtures?

Here are some recommendations for the most common light fixture types:

Table Lamps

  • Use an A15 or G25 shape bulb.
  • Choose an E26 medium base.
  • Opt for a wattage between 40-100W depending on lamp size.
  • So a good all-purpose bulb would be a 60W A15 E26.

Floor Lamps

  • Use an A15 or G25 shape.
  • Choose an E26 medium base.
  • Opt for a wattage between 60-150W depending on lamp height.
  • A 100W A15 E26 is a safe standard option.

Pendant Lights

  • Use an A15, G25, PAR16, or BR30.
  • Choose an E26 medium base.
  • Opt for 40-100W depending on pendant size.
  • A 60W A15 E26 or BR30 E26 works well.

Recessed Cans

  • Use a BR30 or PAR30 flood or spot reflector bulb.
  • Choose an E26 medium base.
  • Opt for 50-150W depending on can size and purpose.
  • BR30 or PAR30 120W bulbs work well for most applications.

Track Lighting

  • Use MR16 bulbs with a GU5.3 bi-pin base.
  • Choose a wattage between 20-50 watts per fixture head.
  • MR16 35W bulbs provide good accent lighting.


  • Use T4, G25, or E12 candelabra base bulbs.
  • Choose a wattage between 15-60W depending on fixture size and number of bulbs.
  • 25W G25 or T4 bulbs work well for most chandeliers.

Bathroom Vanities

  • Opt for smaller G25 or A15 bulbs.
  • Choose an E26 medium base.
  • Stay under 40 watts for the bulb.
  • A 25W G25 E26 bulb provides a nice glow.

Ceiling Fans

  • Use standard A15 light bulb shape.
  • Choose an E26 medium base.
  • Stay under 100 watts so as not to overload the fixture.
  • A 60W or 75W A15 E26 is recommended.

Can I Use a Higher Wattage Bulb?

Sometimes you may wish to use a higher wattage bulb to increase brightness. However, you need to make sure the fixture is rated to handle the increased wattage. Check the fixture or socket for a maximum wattage label. Using a bulb with too high of a wattage can lead to overheating and fire hazards. As a general rule of thumb:

  • Table lamps can often handle 60-100W max.
  • Floor lamps and pendant lights 100W max.
  • Recessed lights 150W max depending on can rating.
  • Chandeliers and sconces 60W max.
  • Ceiling fans 100W max.

If in doubt, stick to the same or lower wattage to be safe. Use multiple bulbs or supplemental lighting like table lamps to increase brightness as needed.

What About Lumens Instead of Watts?

With newer LED bulbs, lumens are a better measure of brightness than watts. Here are some lumens equivalencies:

  • 40W incandescent = 450 lumens
  • 60W incandescent = 800 lumens
  • 75W incandescent = 1,100 lumens
  • 100W incandescent = 1,600 lumens

So choose an energy-saving LED with equivalent or higher lumens to match the brightness you need. Just make sure the LED bulb shape, base, and wattage rating are still compatible with the fixture.

Smart Light Bulbs

Smart bulbs like Philips Hue can be controlled via smartphone and change color. However, you still need to choose the right base and shape:

  • For table lamps, use an A19 E26 bulb.
  • For recessed lights, use a BR30 E26 bulb.
  • For chandeliers, use an A19 or ST18 E12 candelabra base.

The base and shape still need to match the fixture, even if using a smart bulb. Check manufacturer instructions for compatible bulbs and wattages.

Can I Use Lumens Instead of Watts?

Some newer fixtures and lamps specify lumens instead of watts. Lumens measure the total light output rather than energy used. Here is a lumens to watts conversion:

  • 450 lumens ≈ 40 watt incandescent
  • 800 lumens ≈ 60 watt incandescent
  • 1100 lumens ≈ 75 watt incandescent
  • 1600 lumens ≈ 100 watt incandescent

So match the equivalent wattage when choosing the bulb. Just make sure not to exceed any wattage ratings for the fixture itself.

Choosing LED vs CFL vs Incandescent Bulbs

You also need to decide what bulb technology to use:

  • Incandescents are inexpensive but inefficient. Being phased out.
  • CFLs are compact fluorescent lamps. More efficient and last longer. Contain mercury.
  • LEDs are the most efficient and long lasting. Great for accent lighting. Higher initial cost.

For most applications, LED is the best choice long term. Just match the lumens and shape when replacing old bulbs with LED.

Key Takeaways on Bulb Size and Fit

  • Match the bulb base to the socket – E26, E12, GU24 etc.
  • Choose the right shape – A15, BR30, PAR etc.
  • Opt for the proper beam spread and brightness.
  • Consider lumens not just watts.
  • Don’t exceed max wattage or lumens ratings.
  • LED is the best long term option in most cases.

Frequently Asked Questions

Below are some common questions people have about light bulb sizes and fittings:

Can I use a higher wattage bulb than recommended?

Only if the fixture is rated for it. Check for a max wattage label. Using too high of a wattage can cause overheating and fire hazards. When in doubt, stick to the same or lower wattage.

What happens if I use the wrong shaped bulb?

The bulb may not fit properly or direct light where needed. BR bulbs are made for recessed cans, while A shapes suit table lamps. Using the wrong shape can reduce fixture performance.

How do I know which bulb base I need?

Check the socket inside the fixture and match accordingly – E26 for standard medium screw base, E12 for candelabra bases, GU24 for two-pin, etc. Using the wrong base type will prevent the bulb from fitting securely.

Why do some LED bulbs not fit my fixture?

Older fixtures may not be designed for the wider bases on some LED A19 bulbs. Choose slimmer LED bulbs or ones labeled as compatible with existing fixtures.

Can I use a CFL or LED instead of an incandescent?

Yes, provided you match the base, shape, brightness (lumens) and do not exceed the wattage rating for the fixture. CFLs and LEDs operate at lower wattages than comparable incandescents.

How do I choose the right wattage for a fixture?

Check existing bulbs and do not exceed that wattage. If unknown, use lower wattages like 40W for small lamps, 60W for most table fixtures, 100W for large ceiling lights and chandeliers.

Why do some recessed housing say no bulbs over 50 watts?

The housing is only rated for lower wattage bulbs to prevent overheating. Always check fixture labels and instructions to avoid installing bulbs above the listed wattage rating.

What does G25 mean for light bulbs?

G refers to a globe shaped bulb with a diameter of 2.5 inches. The shape helps provide decorative, omnidirectional lighting. Choose G25 bulbs for bathroom vanities, chandeliers, and globes.

What size LED bulb should I use in a lamp?

For a table lamp, choose an A19 or G25 shape LED bulb with an E26 base, and a lumen output equivalent to a 60W to 100W incandescent, depending on lamp size. This will provide good ambient light.


Determining what light bulb shapes, bases, sizes, and wattages you can use largely comes down to matching the specifications of your existing fixture. Read all labels closely, measure diameters if needed, and match the corresponding bulb type and features. Doing so will ensure optimal light quality and prevent any electrical issues. With so many LED options today producing less heat and using less energy, you can easily upgrade most fixtures while still getting the right light output. Just take care to find compatible shapes and bases when switching to more advanced bulb technologies. With the proper bulb in place, you can enjoy the right lighting for every task and setting in your home.