Tire gauges are available at most auto parts stores.
Dial-type gauges are easier to read then pen or stick designs. Tire pressure should be checked cold, first thing in the morning or after the car has sat still for awhile. Recommended tire pressures are for cold tires. Checking tire pressure on a car that has hot tires can result in a pressure difference of up to 5 psi. Look for your tire's recommended air pressure in the vehicle's owner's manual, or inside the driver's side car door or glove compartment.