The regular smoker buys pot in increments of 1/4 of an ounce. 1/4 usually for a social smoker, a 1/2 for a people like me that smoke all the time, and an ounce for people that live in a household with multiple smokers may buy 1-4 ounces at a time, as it is much cheaper ($100 for an ounce, $250 for 4 ounces, on average)
In Tennessee, more than an ounce is a felony. Laws vary greatly by state.
In Nevada, if you are under 21, you can get 1-4 years for possesion of marijuana in any amount under 1 ounce, and it is a felony. If you are over 21, it's a $600 fine with no jail time and required drug treatment program for the same amount. It's only a misdemeanor if you are over 21, and punishable in the same way as a minor traffic violation.