Adding Salt back to a tank.

So i had an ick out break and i lowered my salinity and it helped and the fish are looking healthy again. But now i need to bring the salinity back up to the right levels, how do i calculate how much salt to put in to bring it to normal? I am fine doing the math if someone just gives me a formula. I don't want to mix really salty mixes throw it in the tank test and repeat. I would like to with some accuracy know how much i need to put in. Also my salt mix and my 1/2 cup container raises 1 gallon of water to 1.023.