The tire psi (pounds per square inch) rating is found on the side door jam and in the manual of the car. Most vehicles range from 30 to 35 psi, depending on the size and weight of the vehicle.
The most common location to find the tire specifications is of the driver side B-pillar door jam. The information will be contained on a placard, which will also detail additional information, including the maximum tire pressure allowed.
Because some drivers tend to manipulate the tire pressure according to their driving habits, the placard houses information setting the limits of air pressure at which a tire should operate. It helps in preventing against overinflating the tire, which can cause it to blow out.