Varies from person to person. Oversleeping is bad for you too, which not a lot of people seem to realise.
For me it is usually 7 hours. Get in bed by 10 to 11 and wake up around 6 to 6:30 for work. I usually wake up 10 minutes before my alarm cause I’m so used it.
I find 7-hours is perfect. A weird thing I learned about myself is I'm great with odd numbers of sleep, 5, 7, maybe 9 hours. The even numbers make me tired, 6 or 8 leaves me wanting more sleep. It's probably psychological, but it's true for me.