How much is 0.7 ounces of marijuana?

It shouldn't take a whole ounce unless it's incredibly bad stuff, even then you certainly won't need an ounce before you feel the effects... For a novice smoker you'll most likely start feeling the high after just one spliff (also depending on whether you're smoking it pure or European style, without or with tobacco) or a bong hit or so. Obviously for more experienced smokers it usually takes progressively more.