"PSI" is an acronym that stands for "pounds per square inch," and it is the standard unit of measurement for pressure. When measuring tire pressure, the PSI is equal to the pounds of air pressure being exerted on a 1-square-inch area within the tire.
The normal pressure of a tire is about 32 PSI. However, the ideal pressure of tires can vary with size and brand, so it is important to check the recommended PSI before filling new tires. A vehicle's recommended PSI can typically be found in the owner's manual or on a sticker on the driver's door. A tire should never be filled 5 PSI above or below its ideal pressure, or it may become a safety hazard and increase the likelihood of premature wear or blowouts.