Common Light Bulb Base Sizes: Which is Right for Your Light?

There are 4 most common bulb base types, along with their specific sizes, including the popular E26 and E27 for Edison Screw bases, B22d and B15d for Bayonet Cap bases, G4 and G9 for Pin bases, and G5 and G13 for Fluorescent Lamp bases.

To determine which one is right for your light fixture, consider factors like socket type, wattage, and your preferred lighting style. These will help you choose the correct bulb base size for both functionality and aesthetics.

In this guide, we walk through the 4 different types of light bulb bases, including screw bases, bayonet caps, pin bases, and fluorescent tube connectors. Then, we cover which size works with your fixture, the typical uses for each base, and tips for choosing the right one. Knowing the proper base size helps you avoid returning products and ensures your bulbs perform as expected.

Let's dive in!

Screw Base (Edison Screw - ES)

The Edison screw base, invented by Thomas Edison, is the most commonly used base type worldwide. It’s designed to twist securely into a socket, providing a stable electrical connection. The variety of diameters allows it to fit everything from small table lamps to large industrial fixtures.

7 Popular Sizes of Edison Screw Bulb Types

LED Edison screw bulbs are highly energy-efficient, lasting anywhere from 15,000 to 50,000 hours. Many modern fixtures even come with built-in LED lights, so you don’t need to change bulbs at all.

The color temperature of your E26 or E27 bulb base plays a key role in setting the mood of your room. Warm lights (2700K) create a cozy and inviting atmosphere, while cooler lights (5000K) are ideal for workspaces, such as kitchens, where bright, focused light is needed.

Popular Edison Screw Sizes:

Base Type	Diameter	Common Use	Typical Wattage
E26	26 mm	North American households	40W - 100W
E27	27 mm	European/Asian households	40W - 100W
E12	12 mm	Decorative fixtures	Up to 40W
E14	14 mm	Small European lamps	25W - 60W
E17	17 mm	Appliances	25W - 60W
E39/E40	39-40 mm	Industrial/street lighting	150W - 1000W

E26 and E27 Medium Base

These medium-sized bases are perfect for everyday fixtures like table lamps, ceiling lights, and floor lamps. So, whether you’re replacing a bulb or upgrading your lighting, these bases are the ones you reach for.

The E26 base (26 mm diameter) is most commonly used in North America, while the E27 base (27 mm diameter) serves the same purpose in Europe, Asia, and other regions. The slight difference in size is due to varying voltage standards, but both bases are compatible with incandescent, CFL, and LED bulbs, making them versatile for all your lighting needs.

E26 / E27 bulb bases (26mm / 27mm diameters)

These medium bases support wattages between 40W and 100W, and are compatible with popular bulb shapes such as A19, A21, globe, and even vintage filament styles. The threaded design of these bases ensures a secure fit, so you don't have to worry about your bulbs loosening over time.

Key Features of E26 and E27 Medium Bases:

Specification	E26	E27
Diameter	26 mm	27 mm
Primary Region	North America	Europe, Asia, Africa
Voltage Compatibility	120V systems	220-240V systems
Common Bulb Shapes	A19, A21, globe, vintage	A60, globe, candle
Thread Count	7 threads per 25mm	7 threads per 25mm

E12 Candelabra Base

The E12 candelabra base (12 mm diameter) is the perfect choice if you’re looking to add a touch of elegance to your home with a chandelier, wall sconce, or string lights. Its small size is ideal for delicate, decorative fixtures, where style is just as important as functionality.

E12 bulbs are typically 40W or less, with many available in charming flame-tip or torpedo shapes. What’s even better? The LED versions of these bulbs provide the same lovely look, using only 4-6 watts, which means less energy consumption and longer life.

E12 bulb base (12mm diameters)

These bulbs emit a soft, amber light around 2400K, similar to the gentle glow of candlelight. Perfect for creating a warm, inviting atmosphere in spaces like dining rooms or bedrooms. Plus, you can fit multiple bulbs in tight spaces because of the small base, making it easier to illuminate more areas with a cozy, ambient light..

Key Features of E12 Candelabra Base:

Base Diameter: 12 mm
Common Wattage: 25W - 40W (incandescent), 4W - 6W (LED)
Typical Color Temperature: 2400K - 2700K (warm, amber light)
Popular Bulb Shapes: Flame tip, torpedo, candle
Primary Applications: Chandeliers, sconces, decorative lighting
Thread Type: Fine thread, 7 threads per inch

E39 / EX39 / E40 Mogul Base

The mogul base is the solution when you need lighting that delivers high wattage and reliability. Designed for heavy-duty applications, the E39 and E40 bases are perfect for fixtures that require a strong, stable electrical connection. These bases are often used in industrial settings like streetlights, warehouses, and outdoor spaces where high-output lighting is essential.

E39 Base (39 mm diameter) is the standard in North America, commonly found in streetlights and industrial lighting.
E40 Base (40 mm diameter) serves a similar purpose in Europe and Asia, offering the same robust capabilities but designed to meet regional electrical standards.
EX39 Base: This variation features extended threads, making it ideal for environments with high vibration, specifically large machinery or outdoor streetlight installations.

These bases handle bulbs with wattages ranging from 150W to over 1000W, providing bright, reliable lighting even in the most demanding settings. Thanks to their deeper threads, these bases securely mount bulbs and prevent them from loosening over time.

E39/EX39 and E40 base bulbs (39mm and 40mm diameters)

Key Features of Mogul Bases:

Wattage Range: 150W to 1500W, depending on the bulb type.
Thread Depth: Deeper than standard bases for a more secure fit.
Applications: Streetlights, warehouses, gyms, parking lots, and other high-wattage lighting areas.
Heat Tolerance: Designed to endure high temperatures and demanding environments.

Mogul bases are commonly used in metal halide and high-pressure sodium bulbs, both of which require substantial output for powerful lighting. So, whether it’s lighting a large parking lot or a warehouse, these bases deliver

E14 European Base

The E14 base, also known as the Small Edison Screw (SES), is a popular choice in Europe for decorative and compact lighting needs. Measuring just 14 mm in diameter, this base is typically used in smaller lamps, bedside fixtures, and even appliances. Its compact size makes it ideal for spaces where larger bases wouldn’t fit.

E14 bulbs are commonly found in European homes and are often used in decorative fixtures such as chandeliers, salt lamps, and nightlights. These bulbs range from 25W to 60W, and opting for an LED version provides the same light output with far less power consumption.

E14 base bulb (14mm diameters)

Key E14 Features:

Wattage Range: 25W to 60W (traditional incandescent), 4W to 10W (LED).
Popular Applications:
- Residential: Bedside lamps, hallway lighting, and accent lights.
- Commercial: Table lamps in restaurants, decorative lighting in hotels.
- Appliances: Found in refrigerators, range hoods, and even sewing machines.
- Decorative: Salt lamps, night lights, and seasonal decorations.
Bulb Shapes: Often seen in candle, golf ball, or miniature globe shapes.

E14 is widely available in Europe, but it’s less common in other regions. So, this base is the one you need if you’re using a fixture from Europe or the Middle East.

E17 Intermediate Base

The E17 base, measuring 17 mm in diameter, is a middle ground between the small E12 and the larger E26 bases. It’s perfect for appliances like microwaves, refrigerators, and range hoods, as well as some decorative lighting, specifically Christmas lights. Though not as widely used for general lighting, the E17 shines in situations where space is limited, and a secure fit is crucial.

E17 bulbs' design handles light vibration, which makes them ideal for appliances and fixtures that are subject to movement. Plus, LED E17 bulbs last much longer, reducing the frequency of bulb replacements.

E17 bulb base (17mm diameters)

Key E17 Features:

Diameter: 17 mm (between E12 and E26 in size).
Wattage Range: 25W to 60W, perfect for smaller appliances or specialty fixtures.
Adaptability: Adapters are available to convert E17 sockets to E12 or E26 bases.
Common Uses: Appliance lighting, specialized fixtures, and vintage pendant lights.

In short, the E17 base is ideal for tight spaces, where you need a secure and efficient connection. Though it’s not as common worldwide, it’s a crucial part of many North American appliances

Push and Twist Base (Bayonet Cap - BC)

The bayonet cap bases use a simple yet secure push-and-twist mechanism, which makes installation a breeze. Instead of threading the bulb into the socket, the base’s pins align with slots in the socket, and a quick quarter turn locks it in place. This design, originating from Britain, is popular in many former Commonwealth countries.

3 Common Push and Twist Bulb Bases

One of the most common sizes is the B22d base (22 mm diameter), widely used in the UK, Australia, and several Asian countries. The quick-connect design is great for preventing loosening, even in environments with vibrations, such as in ceiling fixtures or high-traffic areas.

For smaller fixtures, the B15d base (15 mm) is often used, particularly for small lamps and appliances. Additionally, in industrial applications, three-pin bayonet designs provide an extra level of security to prevent bulbs from loosening in high-vibration environments.

Here’s a quick guide to bayonet cap base sizes:

Base Type	Diameter	Pin Count	Common Regions	Applications
B22d	22 mm	2 pins	UK, Australia, India	General household lighting
B15d	15 mm	2 pins	UK, Europe	Small lamps, appliances
B22d-3	22 mm	3 pins	Industrial	Railway, marine applications

Pin Base (Bi-Pin/Pin Base)

Bi-pin bases feature 2 metal pins that fit into matching holes in the socket, providing a secure connection and efficient electrical conduction. This design reduces electrical resistance compared to threaded bases, making it a great option for halogen bulbs, fluorescent starters, and LED replacements.

5 Popular Bi-Pins (Pin Bases)

Smaller bi-pin bulbs, like the G4 base, are perfect for under-cabinet or decorative lighting. Meanwhile, GU10 bases, with their twist-lock design, offer extra security and are commonly found in ceiling spotlights.

For office and commercial spaces, G13 bi-pins are used in fluorescent tube installations, offering reliable performance in larger fixtures.

Here’s a look at popular bi-pin base sizes:

Base Code	Pin Spacing	Common Use	Typical Wattage
G4	4 mm	Under-cabinet, decorative	5W - 35W (halogen), 2W - 5W (LED)
G9	9 mm	Decorative pendants, fixtures	25W - 60W (halogen), 3W - 7W (LED)
GU10	10 mm (twist-lock)	Ceiling spotlights	35W - 75W (halogen), 5W - 12W (LED)
GU24	24 mm (twist-lock)	Energy-efficient fixtures	LED only, various wattages
G13	13 mm	Fluorescent tubes (T8, T12)	15W - 70W per tube

Fluorescent Lamp Base

Fluorescent tubes are equipped with bi-pin bases at both ends. The G5 base, with 5 mm pin spacing, is used for T5 tubes, which are common in modern setups. The G13 base, with 13 mm pin spacing, fits T8 and older T12 tubes.

Each tube slots into spring-loaded sockets, completing the circuit and ensuring the proper starter and ballast functions. These bulbs often use the same base and eliminate the need for a ballast when upgrading to LED tubes.

3 Common Fluorescent Lamp Base for T5/T8/T12 tubes

In industrial settings, twist-lock pin bases provide added security, preventing tubes from dislodging due to vibration. Standardized pin spacing ensures that tubes and fixtures are compatible worldwide.

Here’s a breakdown of fluorescent lamp base sizes:

Base Type	Pin Spacing	Tube Type	Diameter	Common Length
G5	5 mm	T5	16 mm (5/8")	300mm - 1500mm
G13	13 mm	T8	26 mm (1")	600mm - 2400mm
G13	13 mm	T12	38 mm (1.5")	600mm - 2400mm
2G11	4-pin	Compact fluorescent	Various	220mm - 550mm

What Light Bulb Base Size is Right for Your Fixtures?

Key Considerations When Choosing a Light Bulb Base Size

It is important to consider the design of your fixture and the region you are in when selecting a bulb base. Different areas use different standards, and understanding these will help guide your decision.

Socket Type: What kind of connection does your fixture use? This determines which bulb base is compatible.
Bulb Size and Wattage: Ensure the base fits and supports the bulb's wattage. The E26 and E27 bases are designed to handle higher wattages, while the E12 and E14 bases are better suited for smaller bulbs.
Lighting Style: Are you aiming for focused lighting (like spotlights) or ambient lighting (like ceiling fixtures)? This affects your choice of base and bulb.

In the U.S., common bases include:

E26 (for most household lights, specifically pendant and ceiling fixtures)
E12 (for chandeliers and small lamps)
GU10 (for spotlights and downlights)

Meanwhile, in other countries, you might find:

B22d is the standard in the UK for ceiling lights.
E27 is the typical choice in Europe for general lighting and decorative fixtures.

Suggestions for Choosing the Right Light Bulb Base

To make your decision even easier, here’s a quick guide to help you choose the best base size for your fixture:

Base Size (Type)	Advantages	Bulb Compatibility	Best For
E26 (Edison Screw)	Common, easy installation, secure connection	Incandescent, LED, CFL, Halogen	Pendant lights, ceiling lights, table lamps
E27 (Edison Screw)	Similar to E26 but slightly larger, widely used in Europe	Incandescent, LED, CFL, Halogen	European homes, decorative fixtures
E12 (Edison Screw)	Compact size, ideal for decorative fixtures	Incandescent, LED, CFL	Chandeliers, small lamps, holiday lighting
E14 (Edison Screw)	Compact, versatile, easy installation	Incandescent, LED, CFL	Small lamps, European chandeliers, accent lighting
E17 (Edison Screw)	Mid-sized, often used in smaller appliances	Incandescent, LED, CFL	Appliance lighting, smaller lamps
E39/E40 (Edison Screw)	Larger size for heavy-duty fixtures, secure connection	Incandescent, LED, CFL	Industrial lighting, large outdoor lamps
B22d (Bayonet Cap)	Secure twist-and-lock connection	Incandescent, LED, CFL	UK and parts of Asia, ceiling lights, floor lamps
B15d (Bayonet Cap)	Compact, secure fit, dual contacts, stable and secure	Incandescent, LED, CFL	Small fixtures, chandeliers, accent lighting, automotive, small fixtures
B22d-3 (Bayonet Cap)	Triple contact for added security	Incandescent, LED, CFL	Specialized fixtures requiring extra stability
G4 (Bi-Pin)	Small, compact, great for delicate fixtures	Halogen, LED	Decorative lighting, under-cabinet lights
G9 (Bi-Pin)	Compact size, easy installation, stable connection	Halogen, LED	Accent lighting, small chandeliers, table lamps
GU10 (Bi-Pin)	Twist-lock design for secure fit, directional light	LED, Halogen	Spotlights, downlights, track lighting
GU24 (Bi-Pin)	Energy-efficient, compact, twist-lock design	CFL, LED	Energy-efficient lighting for homes and offices
G13 (Bi-Pin)	Standard for long fluorescent tubes	Fluorescent	Offices, workshops, commercial lighting
G5 (Fluorescent)	Small size, compact, efficient	Fluorescent	Compact fluorescent lights, small fixtures
G13 (Fluorescent)	Common for linear fluorescent tubes	Fluorescent	Commercial spaces, offices, industrial lighting
2G11 (Fluorescent)	Four-pin base for compact fluorescent tubes	CFL	Offices, workshops, energy-efficient lighting

Frequently Asked Questions about light bulb base sizes

How do I know what size base my light bulb is?

To identify your light bulb base size, look for codes like E26, E12, or G4 printed near the base.

Alternatively, measure the diameter of screw bases with a ruler or calipers, or check the pin spacing for bi-pin bases. The packaging always lists the base type.

What is a European light bulb base?

In Europe, the most common light bulb base is the E27 medium screw base, used for general household lighting. It has a 27 mm diameter and supports 220-240V systems.

Other European bases include E14 (14 mm screw), B22 bayonet cap, and G5/G13 bi-pins for fluorescent tubes.

What does T5, T8, and T12 mean?

The terms T5, T8, and T12 refer to the diameter of fluorescent tubes, with the "T" standing for "tubular" and the number representing the tube's diameter in eighths of an inch.

T5: 5/8 inch (16 mm) in diameter
T8: 8/8 equal to 1 inch (25 mm) in diameter
T12: 12/8 equal to 1.5 inches (38 mm) in diameter

What if the bulb base doesn't fit the socket?

The bulb base doesn't fit, which means you’re using the wrong base type for that socket.

Ensure that the bulb base size (E26, E12, etc.) matches your fixture's socket size. An adapter is what you need to convert the bases.

Conclusion

Choosing the right base for your light fixture is key to both its function and aesthetics. With this guide, you can confidently select the best bulb base for your needs, ensuring a secure fit and optimal performance.

For unique, Indochinalight's handcrafted rattan pendant lights, the right base enhances both style and functionality, making all the difference in showcasing the beauty of your fixture. Ready to light up your space? The right base is the first step!

IndochinaLight - IndochinaHomeDecor LLC

Email: service@indochinalight.com
Phone: (+1) 307 249 0594
Address: 30 N Gould St Ste. N, Sheridan, WY 82801

Lewis Nguyen

Lewis Nguyen is the CEO & Founder of Indochina Light. With over 5 years of experience in interior design, Lewis is passionate about Vietnamese handicrafts and embraces the Wabi Sabi aesthetic in his creations.

His dedication to blending traditional craftsmanship with modern design has shaped Indochina Light into a leader in the industry, offering unique, eco-friendly handcrafted pendant lights that reflect his vision for beauty in imperfection.

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