A mosquito drinks between 0.001 and 0.01 millilitres of blood per “serving”. To simplify things, lets say the little blood sucker on average drinks 0.005 millilitres of blood each time.
A human body on average contains 5 litres (5000 millilitres) of blood. This means that if one million mosquitos attacked a human at once, they would suck the poor soul dry (5000 / 0.005 = 1000000).
Tip of the day people: If you see a cloud of approximately one million hungry mosquitos coming your way, run. Run like the wind. Your life depends on it.