When the AC on my 1996 stops working it only takes about 1/4 can (2 or 3 Oz) to get it back to functional when I decide to "cheat" and just top it up. If I put a whole can in it would blow the overpressure valve through the hood! ( it only holds 22.08 oz - - a tall can of 134A is 16 oz. A standard "chubby" can holds 12 Oz so if I could get ALL of the gas out of the cans, 2 chubbies would slightly over-fill my 1996 Ranger. In practice, 2 cans works out just about perfect on an evacuated system.
Again - NEVER top up with a "replacement" refrigerant. Only use "replacements" on an evacuated system , and follow the conversion numbers. Some "replacements" for 134A take closer to 2 lbs - if charging with R12 the system holds 1.75 lb (early 1974 R12 system spec) -the system is virtually identical.