Headlight Bulb Size Chart: How to Read the Code
A headlight bulb code identifies the bulb’s shape, base, electrical design, or approval standard. The code printed on the old bulb is often the fastest way to find a replacement, but it is not always enough by itself. A vehicle may use different bulbs for low beam, high beam, fog lamps, daytime running lights, or a combined high-and-low-beam unit.
Use this guide to compare common designations and then confirm the exact application in the owner’s manual, the vehicle’s bulb label, or a reliable parts catalog.
Common Headlight Bulb Designations
Halogen bulbs
- H1: A single-filament halogen bulb commonly used for one beam function. It has a separate electrical terminal and a metal mounting flange.
- H3: A single-filament bulb often found in auxiliary or fog-light applications. The wire connection is part of the bulb design.
- H4: A dual-filament bulb that can provide low and high beam from one housing. It normally has three electrical terminals.
- H7: A single-filament bulb used for one beam function. It has a compact two-terminal base and is not interchangeable with H4.
- H8, H9 and H11: Similar-looking single-filament families with different electrical ratings, bases, and intended applications. Do not substitute one for another solely because the connector appears similar.
- H15: A dual-filament bulb used in some applications for daytime running light and high beam functions.
- H16: A compact bulb family frequently used for auxiliary or fog lighting. Several regional versions exist, so check the base and rating carefully.
- 9005 / HB3: Two designations commonly associated with the same general single-filament bulb family. It is commonly used for one beam function, but the vehicle application must still be confirmed.
- 9006 / HB4: A single-filament bulb family with a different base and beam application from 9005/HB3.
- 9007 / HB5: A dual-filament bulb family for combined high- and low-beam systems.
- 9008 / H13: A dual-filament bulb family used for combined high- and low-beam applications.
High-intensity discharge bulbs
- D1S and D1R: HID bulbs with an integrated igniter. The S version is generally associated with projector optics, while the R version is designed for reflector systems with glare-control features.
- D2S and D2R: HID bulb families that use a separate igniter or ballast arrangement. As with D1 bulbs, S and R versions are designed for different headlamp optics.
- D3S, D3R, D4S and D4R: Later HID families with different electrical systems from earlier D-series bulbs. They should not be mixed with another D-series type unless the manufacturer specifies compatibility.
LED replacement bulbs
LED retrofit products are often sold as replacements for halogen codes such as H4, H7, H11, or 9005. The replacement must match the original bulb’s base and locking tabs, but physical fit does not guarantee a correct beam pattern. Cooling fans, heat sinks, dust-cap clearance, polarity, and vehicle bulb-monitoring systems can also affect installation.
How to Compare Two Bulb Codes
Start with the complete designation, including letters, numbers, and suffixes. A code that looks nearly identical may describe a different base, filament layout, wattage, or optical position.
- Compare the base: Check the locking tabs, flange shape, connector position, and overall insertion depth.
- Compare the filament count: A single-filament bulb cannot replace a dual-filament bulb in a combined-beam headlamp.
- Compare voltage and wattage: Use the rating specified for the vehicle. A higher-wattage bulb can overheat wiring, connectors, or the reflector.
- Check the beam role: Low beam, high beam, fog light, and daytime running light positions may use different bulb types.
- Check suffixes: Suffixes can identify optical versions, color, weather resistance, connector changes, or regional standards.
Bulb Size Chart: Quick Reference
The following chart is a designation guide, not a vehicle-specific fitment list:
- Single-filament halogen: H1, H3, H7, H8, H9, H11, 9005/HB3, and 9006/HB4.
- Dual-filament halogen: H4, H15, 9007/HB5, and 9008/H13.
- HID systems: D1S, D1R, D2S, D2R, D3S, D3R, D4S, and D4R.
- LED replacements: Usually labeled to match the original bulb family, but they require additional fit and beam-pattern checks.
Best Way to Confirm the Correct Bulb
Remove the bulb only after the lamp has cooled and the ignition is switched off. Read the designation printed on the bulb base or plastic housing. If the marking is missing, compare the connector and mounting flange with a replacement guide, then verify the result using the owner’s manual or a trusted fitment catalog.
Do not touch a halogen bulb’s glass envelope with bare fingers. Oil from skin can create hot spots and shorten bulb life. After installation, secure the bulb fully, reconnect the plug, reinstall any dust cover, and test both low and high beam. A bulb that fits loosely, does not lock, or produces an uneven beam should not be used.
Important Fitment Reminder
Bulb designations are standardized references, not a universal guarantee of vehicle compatibility. The same vehicle model can have different headlamps by market, trim level, production date, or factory lighting package. Treat the bulb code as the starting point, and confirm the complete application before buying or modifying the lighting system.