How to say "he's six feet eleven"?
That's another way of saying it. You can say "He's six foot eleven." Usually, you would only say this when you leave out the words "inches" and "tall." Another way to say the same thing would be "He's six feet eleven inches tall." They're pretty much the same, just one is shorter and quicker to say :)
How long is a pole?
It depends. If you are stating how long something is, you say for example: "This pole is 6 feet long." But, if you are using the phrase as an adjective, you say: "The 6-foot-long pole." Hope this helps!