An E12 bulb has an Edison screw cap about 12 mm across, known in North America as the candelabra base and in the UK as CES, candelabra Edison screw. It sits between the tiny E10 (MES) and the familiar 14 mm SES, or E14, and fits neither. So before ordering a replacement, you need two facts from the old bulb: the cap and the voltage.
In British homes E12 is the odd one out. It turns up in garden festoon lights with replaceable globes, in sewing-machine lamps, in indicator and signal lamps, in small night lights and in chandeliers or wall lights brought over from the US or Canada. Each of those runs at a different voltage, which is why buying by cap size alone so often goes wrong.
Measure the thread with a calliper (or a ruler held flat across it). Around 12 mm is E12, around 14 mm is E14, around 10 mm is E10. The IEC gauge puts the E12 thread at a minimum of 11.7 mm across and roughly 15–17 mm long. No ruler? Hold the bulb next to an SES candle bulb: side by side, a 2 mm difference is easy to see.
Then read the cap or the glass. Most bulbs carry a voltage and wattage, such as 240 V 7 W or 12 V 0.45 W. Take a photo of it before you shop. The cap code tells you the bulb will screw in; the voltage tells you whether it will survive.
Letters and numbers after the cap describe the glass, not the base. That is where most confusion starts:
| Shape code | What it looks like | Typical use | Typical light output |
|---|---|---|---|
| B10, B11 | candle with a blunt tip | chandeliers, candle wall lights | 250–450 lm |
| CA10, flame | candle with a bent, flame-like tip | exposed chandelier arms | 150–400 lm |
| C7 | small cone, about 22 mm wide | night lights, small lamps | 40–100 lm |
| G40, G50 | clear globe, 40–50 mm | festoon and party lights | 25–110 lm |
| T (tubular) | slim tube, often around 22 × 55 mm | indicator lamps, appliances | 30–80 lm |
For a sense of scale: a 25 W incandescent gives about 230–270 lumens and a 40 W one about 400–450. A 3 W LED replaces the first, a 5 W LED the second.
The same 12 mm cap is made for 3 V solar string lights, 12 V and 24 V low-voltage garden festoons, 120 V American fittings and 230–240 V mains. A 12 V bulb screwed into a mains festoon fails instantly; a mains bulb in a 12 V set barely glows or stays dark. Check the transformer label or the old bulb and match it exactly.
American lamps need extra care. US bulbs are rated 120 V and burn out at once on UK 230 V mains, and the lamp itself should be checked or rewired by a qualified electrician unless it is marked 220–240 V. A plug adapter changes the pin shape, not the voltage.
Outdoors, choose shatterproof plastic or toughened glass globes and check the rating of the whole set, usually IP44 or higher for garden use. Warm 2200 K globes give the soft café look most people want from a festoon. For a chandelier, 2200–2700 K keeps the candle feel, and a colour rendering index of 90 or more matters when the bulbs are on show.
In sewing machines and indicator panels, the fitting is tight and warm. A traditional bulb is sometimes the only thing that fits; if you switch to LED, check the length and that the bulb is designed for enclosed use. Sewing-machine lamps are usually small mains bulbs of around 15 W; an LED of the same length runs far cooler, which your fabric and fingers will appreciate.
No. E14 (SES) is 14 mm across and is the standard small screw in UK and European lamps. An E14 bulb will not enter an E12 holder, and an E12 bulb sits loose in E14.
No. A19 is a glass shape, the classic American household pear, and it normally comes with the larger E26 base. E12 is a cap size.
B11 describes a blunt candle shape. In North America it usually comes with an E12 cap, but the same shape is also made with E14, so always check the cap code.
Only another E12 of the same voltage. An adapter works in a few roomy fittings, but the safest replacement is a like-for-like E12, ideally LED at a lower wattage.
About 3 W for an old 25 W bulb and about 5 W for a 40 W bulb, judged by lumens rather than watts.
The cap is about 12 mm wide. Overall length depends on the glass: roughly 35 mm for a small candle, 45–55 mm for a C7 or indicator tube and 65–75 mm for a G40 globe or slim filament tube.
Only those labelled dimmable, used with an LED-compatible dimmer.
More on other caps and bulb types is in light bulbs. If your cap turned out smaller still, read about E10 bulbs.
