Sleep - How much is enough?

Apologies, it seems certain this has been done before but my search ability is poor today.

I constantly read that the correct amount of sleep is as important as healthy eating etc etc. And it’s generally accepted that the amount of sleep required varies by individual.

So, how do you determine how much sleep a person needs? And what factors influence this variation?

Yeah i know “If you’re tired you need more” seems like an obvious answer but i believe some people (me one of them) find getting up in the morning difficult no matter how much they sleep and being tired or lethargic during the day can be due to many other reasons.

So, how do i know how much i should sleep?

Trial and error?