On the main contract you lose/make $50 everytime wheat moves $0.01, however on the mini contract you only lose or make $10 every time wheat moves $0.01
However you can also used contracts for difference (CFD's) to trade wheat. With these contracts I think you lose or make $1 every time wheat moves $0.10. Thus you can buy 5 or 10 etc to suit yourself. Also with CFD's you only need to put up 3% margin of what you purchased.