Final answer:
The average length of the menstrual cycle is 28 days, but it may vary from 21 to 45 days, with the menstrual period lasting from two to seven days.
Step-by-step explanation:
The average length of the menstrual cycle is 28 days. This is recognized as the standard length used to identify the timing of events within the cycle. However, it's important to note that the length of the menstrual cycle can vary significantly among individuals and even from month to month for a single individual, typically ranging from 21 to 45 days. The menstrual period itself, also known as the menses phase, typically lasts about five days but can range from two to seven days.