Sleep cycles are roughly 90 minutes and the average person requires 4-5 to feel fully rested. So between 6 - 7.5 hours sleep.
If you want to figure out how many cycles you need, when you get an opportunity at a weekend, Sleep but don't set your alarm, then do that math.
If say it turns out you need 4 cycles then what you want to do is figure out when you want to get up (say 6 am) count your 4 cycles back (midnight) and stick on an extra half an hour (11.30) which is when you should go to bed so you ideally wake up towards the end of a cycle. If your alarm is waking you and you're bleary-eyed and a mess that's usually a sign of either not enough sleep cycles or being woken up in the middle of a cycle (when you are in deep sleep).
When you go to bed you want to avoid any possible interference from light sources such as phones, lights outside which will inevitably interfere with you falling asleep (also try using those night light setting on your phone/PC to tone down the blue light as your evening progresses) . You can get pretty comfortable formed sleep masks these days that aren't super expensive and do a great job in this regard (use one for the last few years and it's an essential).
I highly recommend either of these two books: -
Night School: Wake up to the power of sleep eBook : Wiseman, Richard: Amazon.co.uk: Books
www.amazon.co.uk
Buy Why We Sleep: The New Science of Sleep and Dreams 1 by Walker, Matthew (ISBN: 9780141983769) from Amazon's Book Store. Everyday low prices and free delivery on eligible orders.
www.amazon.co.uk
The first is pretty accessible in terms of advice, whereas the second goes into a lot more detail regarding the science as well as why you should endeavour to get a good nights sleep.
Matthew Walker has been on a couple of Podcasts
A lack of sleep is associated with all types of diseases, including Alzheimer's and cancer.
www.kevinrose.com
