Ways to figure this out are…
The owners manual
You first need to figure out what is the appropriate size of your cars headlight bulbs. The first step is to figure it out by looking at the cars user manual (if you still have one).
Assuming you got one, browse and search for the “lighting” section to see replacement bulb specs.
IF this fails OR you just need to verify… go to option #2 which is… internet.
You can take the harder rout by going to forums and seeing what others are installing in their cars. Or, you can go to websites like AutomotiveBulbFinder.com and search the right bulb size.
I can’t stress enough that almost every car has its unique requirements. Some automobiles need different sizes bulbs for low and high beam lights.
A surefire way to verify any question you have about yours cars bulbs, is to call your local auto-parts store (AutoZone, Advanced Auto Parts, O’Riley’s… etc).
After you got the right size for your bulbs, figure out if your replacement bulbs are Halogen, Xenon or LED.
Here are the three options:
Halogen – Most common and cheapest option with decent light output. Their lifespan tends to be quite long, but the energy they use tends to be wasted through heat.
Xenon/HID – The brightest of them all, working quite well in projector and reflector housings. They are the most expensive option and can cause a lot of glare to other drivers.
LED – Use far less heat to operate than HID’s or halogens. Their brightness levels are between halogen and Xenon bulbs. When it comes to longevity, they can last the longest (by a good margin).
CAUTION: It’s important to use the correct type of bulb. Failing to do so can result in overheating of bulbs, headlamp housing and melting of the wire connections.