[header] How to fill air in a car's tires [title] Buy a tire pressure gauge. [step] Look for the tool at an auto-parts store-something like napa, autozone, checker, kragen, o'reilly, or canadian tire. Pocket gauges are inexpensive and portable. 
Prices range from $5 for a basic gauge to more than $30 for one that is digital, has an air-release button, or even talks. There are two types of pocket gauge: dial-type and pencil-type.