2003 Mazda Protege how much fluid is need

My transmission was dragging I never check the oil for the transmission sadly an after seeing it was dragging I checked it an it was showed hardly any fluid so I put three qts but I'm still seeing it's a lil low even though the cars running fine now an I'm still unsure of how much fluid it takes an I'm also seeing no leek so wondering where did it all go too if the vacuum has anything to do w it