As your text notes, "When it comes to sleep, the expression 'one size fits all' does not apply" (p.123).  This is especially true of students who often must go without sleep to meet the next day's deadline.  But there is a way to estimate your own sleep needs by keeping a sleep log.

To do this, record the time you go to sleep and the time you get up each day for at least two weeks.  Make certain that you include any naps you take during a day, even if they seem to be only a few minutes long.  Naps taken during the weekend are especially important because many of us use the weekend to catch-up on the sleep we've missed during the week.  Record any unusual events which might have forced you to stay up later than longer (like exams and papers) or sleep longer than usual (like a cold or other illness);  these events will interfere with obtaining a sense of your typical sleep needs.

At the end of two weeks, review your sleep log.  Your "sleep need" is roughly equal to the average (total hours slept / number of days) hours you've slept over that period.  For most people, this average is between 7 to 10 hours/day although a large number of healthy people can function with much less sleep, while others need more sleep.  After reading the text, you should conclude that your figure is only an estimate and many factors including growing older, stress, illness, changes in work conditions, lifestyle, and even changes in where you sleep can influence your sleep requirements.  But as a general rule, if you are sleepy for significant periods during the day, you need more sleep!