Am I getting enough sleep?

Getting enough sleep is always a problem for me. I love to stay up late, sometimes squeezing some late night time for myself before I have to go to sleep and then wake up the next day for the daily grind. Lately, though, I've realized that I might be getting enough sleep at around 7 hours per night. For whatever reason, 8 hours has always been the magic number for me, but this WebMD article says that the average is 7 to 8 hours. To test what works best, I might record my sleep hours and how I feel in my exercise journal and then analyze the results.