To find the correct amount, you must consult your vehicle's owner's manual. This manual will specify the refrigerant type (it's likely R-12, but could be R134a if it's been converted) and the correct charge amount. Alternatively, you can find this information by searching online using your specific Cavalier's Vehicle Identification Number (VIN). Many online parts stores allow you to look up your vehicle by VIN.
Caution: Working with refrigerants requires specialized equipment and knowledge. Improper handling can be dangerous and harmful to the environment. It's best to have an automotive professional service your A/C system.