# How to Read a Tire Gauge

by John Stevens J.D.

Maintaining a tire's air pressure will ensure that the tire will operate at its peak efficiency. A tire gauge is used to measure this pressure. Most tire gauges provide two different units of measure: psi and kPa. The term psi, or pound-force per square inch, is the unit of measure most commonly associated with automobile and motorcycle tires. The term kPi, meaning kiloPascal, is a unit of measure commonly used for smaller tires, such as those for bicycles. The psi reading on the gauge is usually marked between 0 and 120, while the kPa reading is generally marked between 150 and 800.

Position the circular portion of the tire gauge over the tire's valve stem. The valve stem is the rubber piece located through the exterior of the tire's wheel. Most valve stems have a small rubber cap located at the tip of the stem. Remove the cap by twisting it in a counterclockwise direction.

Take a reading of the tire's pressure with the tire gauge. Push the tire gauge onto the tip of the valve stem. It's normal to hear air escaping from the valve stem when fitting the gauge into place. The tire gauge should be pressed straight onto the stem as opposed to at an angle to minimize the loss of air and to acquire a proper reading. If using a mechanical gauge, ensure that the bottom of the gauge is free from obstruction as a plastic measuring instrument will slide out of the bottom of the gauge's housing.

Determine the tire's pressure by reading the gauge. If using a mechanical gauge, the measured pressure is found at the point where the plastic measuring instrument meets the base of the gauge's housing. For example, if the first number that appears just below the gauge's housing is 40 psi, the air pressure within the tire is 40 pounds of force per square inch. If using a digital gauge, the tire's pressure will be displayed on the digital screen.