Car Bulb Size Chart & Fitment Finder (UK)
Replacing a blown bulb is one of the simplest jobs on any car, but only if you order the right fitment. The same socket can take very different bulbs, and a wrong base will not seat or connect. This UK reference chart lists the most common car bulb fittings, their base codes and typical uses, so you can identify yours with confidence. When you are ready, browse our full automotive light bulbs collection for matching replacements.
Common car bulb size chart
The table below covers the bulbs found on the vast majority of modern and older UK cars. "Base" is the connector type, which is what determines whether a bulb physically fits.
| Bulb code | Base / cap | Typical use |
|---|---|---|
| H1 | P14.5s (single pin) | Headlight (high or low beam, single-filament projector) |
| H3 | PK22s (with lead) | Fog light, some auxiliary driving lamps |
| H4 | P43t (three-pin) | Headlight, dual-filament (high and low beam in one bulb) |
| H7 | PX26d (two-tab) | Headlight, single beam (separate high/low bulbs) |
| H8 | PGJ19-1 | Fog light, some daytime running lamps |
| H9 | PGJ19-5 | Headlight high beam (high output, single filament) |
| H11 | PGJ19-2 | Headlight low beam or front fog light |
| HB3 (9005) | P20d | Headlight high beam |
| HB4 (9006) | P22d | Headlight low beam or fog light |
| 501 (W5W) | W2.1x9.5d (wedge, capless) | Sidelight, number plate light, interior |
| 382 (P21W) | BA15s (single-contact bayonet) | Indicator, reverse, single-filament brake/tail |
| 380 (P21/5W) | BAY15d (offset-pin bayonet) | Combined brake and tail light (dual filament) |
| 207 (R5W) | BA15s (single-contact bayonet) | Sidelight, number plate, interior |
| 581 (PY21W) | BAU15s (offset-pin bayonet, amber) | Indicator (amber, offset pins to prevent misfitting) |
| 239 (festoon C5W) | SV8.5 (festoon) | Interior, number plate, courtesy light |
Understanding the codes
Two numbering systems are used in the UK, which causes most of the confusion. The "H" and "HB" codes (H1, H4, H7, HB3, HB4) are the international standard for headlight and fog bulbs. The three-digit "trade" numbers (501, 380, 382) are the long-established UK retail codes for smaller bulbs. Many bulbs therefore have two names: a 382 bulb is the same as a P21W, and a 501 is the same as a W5W. Both refer to identical parts.
How to find your bulb size
There are four reliable ways to identify the correct bulb fitment for your car.
- Read the old bulb. The code is usually printed on the glass or the metal base. Remove the blown bulb and read it directly; this is the most accurate method.
- Check the handbook. The owner's manual lists every exterior bulb type for your model, often with a diagram of each lamp unit.
- Look at the housing. The bulb type is sometimes moulded into the rear of the headlight or lamp assembly near the connector.
- Use a registration lookup. Many UK bulb retailers offer a number-plate finder that returns the exact fitments for your vehicle.
If a headlight unit itself is damaged, cracked or fogged rather than just the bulb, you may need a complete headlight assembly. For front fog lamps, our fog lights collection covers both bulbs and complete units.
Headlight bulbs: single vs dual filament
One of the most important distinctions is between single and dual-filament headlight bulbs. An H4 is a dual-filament bulb, carrying both the dipped and main beam in a single unit, which is common on older cars and motorcycles. By contrast, an H7 system uses separate single-filament bulbs for dipped and main beam, so a car with this layout needs two bulbs per side. Never try to substitute one for the other; the bases differ and the beam pattern will be wrong.
Why bases matter more than wattage
The base, or cap, is what physically locates and connects the bulb. A 382 and a 380 look similar but have different pins (single-contact versus offset twin-contact), so a 382 will not work as a combined brake and tail bulb. Likewise the amber 581 (PY21W) has deliberately offset pins so it cannot be fitted the wrong way round. Always match the base code first, then confirm voltage (12V on virtually all cars) and the correct wattage.
Indicator, brake and sidelight bulbs
Small bulbs cause more roadside confusion than headlights because so many look alike. Use these rules of thumb:
- Sidelights and number plate: usually 501 (W5W) capless wedge or 207/233 bayonet.
- Indicators: 382 (P21W) amber, or 581 (PY21W) where an amber bulb sits behind clear glass.
- Brake and tail combined: 380 (P21/5W) dual-filament with offset bayonet pins.
- Reverse and single brake: 382 (P21W) single-filament bayonet.
When in doubt, remove the existing bulb and match the printed code exactly. Getting the base right first time saves a return trip and keeps your car road-legal. Browse the full range in our light bulbs collection once you have confirmed your fitment.
Frequently asked questions
- What is the difference between H7 and H4 bulbs?
- An H4 is a single dual-filament bulb that produces both dipped and main beam, common on older cars. An H7 is a single-filament bulb, so cars using H7 have separate bulbs for dipped and main beam. The bases are different, so the two are not interchangeable.
- Is a 382 bulb the same as a P21W?
- Yes. The three-digit number (382) is the UK trade code and P21W is the international code for the identical bulb. It has a single-contact BA15s bayonet base and is used for indicators, reversing lights and single-filament brake or tail lights.
- How do I find out which bulb my car needs?
- The quickest way is to remove the blown bulb and read the code printed on its glass or base. You can also check the owner's handbook, look for a moulding on the rear of the lamp unit, or use a registration number-plate bulb finder offered by many UK retailers.