Everyone is different, which can make it hard to know what “normal” even means. However, there is an average, or range of typical characteristics. For example, a “normal” period (or menstrual flow) may:

• Occur every 28 days
• Last for 4 to 5 days
• Result in a total blood loss of 35 mL to 40 mL (2 to 3 tablespoons)
• Have blood clots that are smaller than a quarter and occur only occasionally, toward the beginning of your cycle 

According to the objective standard for measuring HMB, women with HMB may lose 80 mL of blood (5 to 6 tablespoons) or more during their period and may have bleeding that lasts longer than 7 days.

Your period may be heavy if you:

• Soak through 1 or more pads or tampons every hour for several hours in a row
• Need to wear more than 1 pad at a time to control your bleeding
• Need to change pads or tampons during the night
• Have periods with blood clots that are the size of a quarter or larger
• Have periods that last more than 7 days
• Have a heavy flow that keeps you from doing the things you would normally do
• Have constant pain in the lower part of the stomach during your period
• Feel tired, lack energy, or experience shortness of breath

Some of the possible causes include:

• Uterine-related problems
• Hormone-related problems
• Other illnesses or disorders