To find the correct amount, you must consult your vehicle's repair manual or a reliable online parts database (like AutoZone, Advance Auto Parts, etc.) and search by your vehicle's VIN or specific compressor model number (usually found on a tag on the compressor itself). The correct oil type and quantity will be specified there.
Attempting to add the wrong amount or type of oil can severely damage your AC system. It's best to get this information definitively before adding any oil.