It's totally impossible to count the total user of bitcoin.
In one way bitcoin is anonymous and in another way in bitcoin world hardly few user usages real info for creating bitcoin wallet. And 1 user usage 1 to 2 or more wallet so it's quite unpredictable to figure out the exact number of bitcoin user. If one want to know then he might have to conduct world wide census.
even with consensus or survey can't give you the right number of people using bitcoin because there's still a big chance you will get the wrong answer,and there's always someone who hiding and keep silence so it's not a good solution i guess, i'm still in my opinion that counting the actual number of people using bitcoin is impossible