I don't think the correct question is how much do you allocate as much as it is how much do you risk. I might ALLOCATE 100% of my capital to a trade but only have a defined risk of 1% of my capital. Maybe that is your question... I allow every trade to lose 2.2% of my total capital. Of course most my trades aren't losers (or I wouldn't have any capital left). And you shouldn't discuss risk without discussing reward. For example, I allow my reward to reach as high as 3.8% of my capital.