Step 1. Purchase a tire gauge.
Tire gauges are small enough to fit in your glove box, and they're a handy tool to have. The newer digital tire gauges can be more accurate—and easier to read—than the older ones. If you don't want to purchase a gauge, you also can go to the air pump at a gas station, which usually has a gauge on the hose. That's convenient, because if you find that your tires need air, you're already there.
Step 2. Discover the proper air pressure for your car
Tire pressure is measured in pounds per square inch, or PSI. You can often find the right PSI for your vehicle on a yellow sticker inside the driver's-side door jam, or you can consult your owner's manual. Remember, the ideal air pressure may be different for the front and rear tires.
Step 3. Remove the air valve cap from your tire.
It's easy to lose this little valve cap. Be sure to place it in your pocket or someplace where it will not roll away or quickly disappear.
Step 4. Press the tire gauge against the open valve stem
You will hear a hiss of air as you press down. Don't be concerned; this is normal.
Step 5. Read the tire pressure
on the gauge
The number will appear on the dial or digital screen on the tire gauge. Compare this number with the recommended tire pressure for the tire. If it's too low, you can add air. If the pressure is too high, you can let air out of the tire.