The amount of freon i need to put in my 1991 toyota corolla ?

Well in that year they used r12 refrigerant ! today they use r134a refrigerant they are not interchangable if you have already converted to r134a they you can call toyota and ask for specific amount although you really dont need to know all you need is a can of r134a with a gauge on it if it
75-80 degrees outside the pressure should be between 40-45 pounds if its 85-90 degrees between 45-50 pounds on the low side were you add it so basiclly keep adding till those pressures are reached

please do not add r134a if you have not had system converted over from r12