It was said at some point to be 3%. Anywhere in 2-5% is plausible. Doesn't take much; a nearly-empty stage weighs next to nothing in comparison to a fully-loade

It was said at some point to be 3%. Anywhere in 2-5% is plausible. Doesn't take much; a nearly-empty stage weighs next to nothing in comparison to a fully-loaded stack. In fact, even with only one engine at minimum throttle, the the F9R-1 stage still has a thrust significantly higher than its weight. Thus the "hover-slam" description of their landing mode: they try to slow down to just above 0 at just the right altitude. Quite a bit of precision required.