As far as I am informed, the amount of sleep one needs varies from person to person. I am no expert but I did read some stuff about it. Also on the whole there is not done that much research about sleep.

I did test it out for myself. Without caffeine-intake my body regulates to a 7,5 hours sleep patern, no alarm-clock needed. With caffeine (2 cups of coffee + a tea) and alcohol (2 beers or so) intake I need ~10 hours sleep per night.