Car bulb numbers explained
Every bulb in a car has a number that tells you the base, the filaments and roughly the size. Learn a handful of them and you can buy the right LED every time.
The common rear bulbs
- 3157 / 3156: plastic wedge base; 3157 has two filaments (tail + brake), 3156 one.
- 7443 / 7440: T20 wedge; 7443 dual, 7440 single.
- 1157 / 1156: metal bayonet; 1157 dual with offset pins, 1156 single.
- 921 / 912: T15 wedge, usually reverse and third brake lights.
The small interior bulbs
- 194 / 168 / T10: small wedge for dome, map, plate and markers.
- Festoon (DE3175, 211-2, 6418): double-ended, measured tip to tip.
- BA9S: mini bayonet for gauges and maps.
- T5 / 74: miniature wedge behind the dash.
What the letters mean
Suffixes describe the glass or filament, not the base: A or NA means amber, K means a heavier-duty socket design, LL means long life. A 3157A and a 3157K both take a 3157 LED bulb; just choose the LED colour you need.
How to find yours
Look at the base of the old bulb — the number is usually stamped on it. The owner's manual lists every bulb in the specifications section. If you have neither, search your year, make and model with the lamp name.
