Get a Gauge
A simple tire air pressure gauge, available at most auto parts stores, for a few dollars, is adequate for the job. You do not necessarily need a digital air pressure gauge. If it is worth the $14 to $15 to you, a digital pressure gauge is easy to read and accurate. However, you should consider whether it will require batteries, and whether this would prevent you from using it.
Again, a standard pressure gauge that measures pounds per square inch (PSI) and fits easily in the glove box of your vehicle, is sufficient. Do avoid ultra-cheap models that may not give a proper reading.
As for a source of air, many gas and service stations have air available for 50 cents or so. Some of these air machines have gauges on them, and if you have no other means of measuring the pressure of your tires, these will work. However, they are typically beat and inaccurate, so have your own gauge to ensure the proper PSI for your tires and vehicle.
Click Here For More!