Bulb size and base: the guide to choosing correctly
This article is also available in French: Taille ampoule
Read the code on the base: the letter indicates the type of connection (E for a screw base, G for pins) and the number indicates the dimension in millimeters. An E27 measures 27 mm for the screw, an E14 measures 14 mm. Compare this code to the one engraved on your lighting fixture.
How to know the size and base of your light bulb?
Turn the bulb over and read the reference near the base: a letter (E, G, GU, B) followed by a number. The letter indicates the connection, screw or pins; the number gives the diameter of the base or the gap between the pins, in millimeters. This same code appears on the fixture's socket.
Every product page in our collection of designer bulbs displays this code, which avoids mistakes when replacing a burnt-out bulb.
How to read a bulb
Three pieces of information matter. The base (E27, G9, GU10) controls the mechanical compatibility. Lumens indicate the amount of light produced. Watts, since the switch to LED, now only measure consumption. To understand all about the labeling, see the different types of light bulbs.
Then there is the tint, expressed in kelvins: around 2700 K for warm light, above 4000 K for a cool white. This is the criterion that changes a room's atmosphere, as explained in our guide on white or yellow light.
How to know the size of a socket
The type is often molded into the socket base or printed near the cable. If not, measure: a 27 mm thread corresponds to an E27 socket, 14 mm to an E14. For pins, it is the spacing that matters: 9 mm for a G9, 4 mm for a G4.
Having doubts about the exact base before ordering your bulb? Check compatibility in a few minutes, or ask our team for advice and they will verify it with you.
E27 or E14: how to recognize the right base?
Look at the diameter of the screw thread. An E27 has a 27 mm screw base, typical of large standard bulbs; an E14 is 14 mm, thinner, reserved for flame-shaped and small accent lamps. Both screw in: only the diameter distinguishes them at a glance.
Based on a survey of 33 pendant lights in our catalog as of September 22, 2026, the E27 base equips 42% of items, G9 27%, G4 24%, and E14 15%. The Design Bulb collection has 282 references on that same date, and this sample is 100% LED, with CE certification.
E27 bulb size
The E27 is the large screw base, the most common connection for pendant lights, floor lamps, and table lamps. Its 27 mm diameter accommodates both standard shapes and decorative globes. Find compatible models among our E27 base bulbs.
E14 bulb size
The E14, or "small Edison screw," is used for thinner fixtures: wall lights, branch chandeliers, bedside lamps. Its 14 mm diameter often requires a small flame-shaped or spherical bulb. Our selection is reviewed by buyers, whose feedback remains visible on the Designix Google profile.
Our designer bulbs, categorized by base
What are the different sizes and shapes of bulbs?
A letter describes the curvature, a number gives the diameter in millimeters. An A60 is the standard 60 mm shape; a G denotes a globe or pin base; a C indicates a flame shape. The base, meanwhile, is read separately: G9, G4, and GU10 refer to pin spacing.
Standard bulb size (A60)
The A60 measures 60 mm at its widest point by approximately 110 mm in height, on an E27 base. This is the format used by the majority of pendant lights and floor lamps; it is also the easiest to replace when changing a fixture.
G9 bulb size
The G9 is a two-pin base with 9 mm spacing, without screws. It is found on small, very bright capsules for wall lights and compact ceiling lights. Its reduced size, just a few centimeters, allows it to fit into discreet diffusers where an A60 would not fit.
GU10 bulb size
The GU10 is a bayonet spotlight: two lugs that you push in and turn a quarter turn. It is the base for recessed and track spotlights. To remove it, follow the method for changing a recessed spotlight bulb.
A classic bulb can be replaced by an LED with the same base, provided you target an equivalent number of lumens rather than watts. For adjustable lighting, check for the dimmer-compatible mention before installing a dimmable bulb, and navigate the transition with our guide on switching entirely to LED.
Which base for your bulb? Run the diagnostic
Three questions about your fixture and usage are enough to identify the right base and shape, without taking anything apart.
Which base does your fixture use?
In stock · shipping costs shown at checkout · up to 30% off in your cart
Ready to turn inspiration into reality?
Tell us about your room, your style and your budget, and we will show you the pieces that truly suit your project.
Get guidance in 30 seconds →
