AP Laterite comes with a reccomendation to use 1 oz per gallon, and I've always heard of people doing just that. It is a very soft dusty red rock which can really cloud the water. Its best to mix the laterite with about half of the gravel you will be using at the bottom of the tank and then cap this with the other half of the gravel to keep the laterite from clouding the water.
Instead of spending so much money on laterite, you would do much better to buy Seachem Flourite instead. (And you would save a lot of money too!)