Margaret Thatcher is famously said to have slept for only four hours a night. It isn't easy to ascertain when Baroness Thatcher first referred to her minimal sleep schedule, but the figure of four hours has passed into lore. People use it as a benchmark of endurance, often jokingly referring to those who need much more. There is no correct amount of sleep. The only rule is to sleep long enough to feel refreshed when you wake up.