There is no specific number, Azhar, as the others so rightly say.
But there are averages; adults need either 6, 7, or 8 hours.
Speaking for myself, I can't establish how much I need; it's always varied according to my circumstances. If I don't feel tired throughout the day, and fall asleep easily at bedtime, then I'm getting the exact amount of sleep I need.
I saw an interesting documentary on this topic a couple of years ago. Apparently, according to statistic, the particular type of individual that NEEDS 7 hours lives longer. Of course, if I only need 6 hours, forcing myself to sleep 7 will not prolong my life :)