Poliquin recommends .44 g/kg of weight off the top of my head I believe. About 40g for a 200 lb guy, and he says you can take half of that and still see decent results. I find he's pretty spot on with advice. I like to take them DURING the workout as opposed to pre post. I'd say mimimum of 15-20 g, but weight, training volume and other peri-workout nutrition will affect this as well.