It’s widely accepted that the average person loses between 30 and 40 milliliters, or two to three tablespoons, of blood during menstruation. But some research suggests that this figure may actually be closer to 60 milliliters, or about 4 tablespoons.

The span of “normal” blood loss is wide, so some people may have periods that are lighter or heavier than what’s considered average. If you aren’t experiencing severe cramping, nausea, or other side effects, your individual amount of blood loss is likely normal.

If you want to figure out where you fall on the menstrual spectrum, read on. We’ll walk you through how to calculate your monthly blood loss, symptoms to watch for, and when to see your doctor.

You expel more than just blood during menstruation. Your menstrual fluid also contains a mix of mucus and uterine tissues, which can add volume to your overall fluid loss. That’s what makes measuring blood loss tricky.

But it’s definitely possible. The hygiene products you use can help you get a rough estimate of your overall flow. And if you want an accurate account of pure blood loss, math is on your side.

If you use menstrual cups

One of the easiest ways to measure fluid loss is with a menstrual cup. You don’t have to deal with absorption issues. Some cups even include volume markings for easy reading.

Depending on the brand and type, your menstrual cups may hold anywhere from 30 to 60 milliliters at a time. If your cup doesn’t have volume markings, you can research the manufacturer’s website to find out more.

When it’s time to empty your cup, take note of how much fluid it contains. You can record this as a note in your phone or keep a log. Then empty, wash, and reinsert as usual.

Continue to update your log for your next three or four periods. This should give you enough data to determine your average menstrual loss per day and per week.

You may find that your entire period loss is greater than 60 milliliters. That’s because tissue, mucus, and uterine lining add volume to your flow.

If you use tampons, pads, or period underwear

It’s a bit harder to measure total menstrual loss when you use absorbent tampons, pads, or period underwear, but it can be done.

First, take into account the item’s fully soaked capacity. Regular tampons, for example, hold 5 milliliters of fluid. Super tampons hold double that.

If you lose 60 milliliters during your period, you may soak through 6 to 12 tampons depending on the size you use. If you lose half of that, you’ll likely use fewer.

You can keep a log to help you get a better idea of how much you’re losing. You should note:

  • what product you’re using and its size
  • how often you have to change it
  • how full it is when you change it

Logging this info for your next three or four periods will give you enough data to calculate a reasonable estimate.

If you can help it, avoid fully soaking an absorbent product. Pushing a tampon or other product to its limit may result in a leak or other unwelcome side effects. The general rule of thumb is to change tampons, pads, and underwear every four hours.

If you want to calculate the actual blood content

First, it’s important to understand one very important element of menstrual flow: You’re not only losing blood.

One study found that a period flow is 36 percent blood and 64 percent other elements, such as:

  • tissue
  • uterine lining
  • mucus
  • blood clots

With this in mind, you can multiply your total loss by 0.36 to determine the approximate amount of blood you’ve lost. Subtracting this figure from your total loss will give you the amount of other materials.

For example, if you collect 120 milliliters of menstrual fluid, multiply that by 0.36 to get a total blood loss of 43.2 milliliters. That’s well within the “normal” range of 30 to 60 milliliters.

If you subtract 43.2 milliliters from 120 milliliters, you find that your menstrual flow contained 76.8 milliliters of other components.

When is bleeding considered heavy? | When is bleeding considered heavy?

Some guidelines say a period is “heavy” when you lose 60 milliliters of blood; others put the number higher, closer to 80 milliliters.

Heavy bleeding, or menorrhagia, isn’t always a cause for concern. Treatment typically isn’t necessary unless it’s interfering with your daily life or you’re experiencing other symptoms.

See your doctor if you:

  • soak through one or more tampons, pads, or cups per hour for several hours
  • need to use double protection, such as a tampon and a pad, to prevent leaking
  • bleed for more than seven days
  • pass blood clots larger than a quarter
  • have to restrict daily activities because of your period
  • experience, fatigue, shortness of breath, or other signs of anemia

If your menstrual flow is consistently heavy, it may be a sign of an underlying condition or the result of a medication you’re taking. You’ll typically experience other symptoms in addition to heavy bleeding. Here’s what to watch for.

Intrauterine device (IUD)

An IUD is an implantable contraceptive. You may experience heavy bleeding, cramping, and back pain for the first couple of days after insertion. Your monthly period may be heavier, longer, or otherwise irregular for the first 6 months.

Polycystic ovarian syndrome (PCOS)

PCOS is a common hormonal condition. It affects how your ovaries work and can cause weight gain, irregular periods, and unwanted hair growth on your face, chest, arms, back, and abdomen.

Endometriosis

Endometriosis occurs when the tissue that typically grows inside of your uterus begins to grow outside of your uterus. This can cause bleeding between periods, general pelvic pain, and pain during sex.

Pelvic inflammatory disease (PID)

PID is an infection in your uterus, fallopian tubes, or ovaries. It can cause irregular bleeding during or between periods, severe abdominal pain, and painful urination.

Fibroids

These noncancerous tumors develop in the muscles of your uterus. They can also cause pain in your lower back and abdomen, difficulty emptying your bladder, and constipation.

Polyps

Like fibroids, polyps are noncancerous growths that develop in the lining of your uterus or cervix. They prevent uterine muscles from contracting, which prevents uterine lining from shedding properly. This can lead to bleeding between periods, shorter or longer periods, and other menstrual irregularities.

Adenomyosis

In people with adenomyosis, uterine tissue embeds itself into your uterine walls rather than sloughing off with menstrual flow. In addition to heavy, prolonged periods, this can cause large blood clots, general pelvic pain, and pain during sex.

Hypothyroidism

If your thyroid is underactive, it isn’t producing enough hormones to properly regulate all of your body’s functions. This can affect menstruation, as well as cause unexplained weight gain and temperature sensitivity.

Bleeding disorders

Bleeding disorders can prevent your blood from clotting. This could lead to heavy menstruation, heavy bleeding after cuts or scrapes, unexplained nosebleeds, and frequent bruising.

Certain medications

Anticoagulant medications also prevent blood clots. This can lead to easy bruising, bleeding gums, and black or bloody stool. The same is true for chemotherapy medications.

If dealing with irregular symptoms, you may find it helpful to:

Keep a record

If you suspect you’re bleeding more than you should be, track your period for a few months. You could use a period tracker app or keep a log. Be sure to note when your period begins and ends, how often you change your cup or absorbent product, and whether you’re experiencing other symptoms.

Take ibuprofen

Ibuprofen (Advil, Motrin) contains an ingredient that can help decrease your blood flow, while taking the edge off of your cramps.

Use a compress

You may also be able to soothe cramping muscles by applying a heating pad or sitting in a warm bath.

Drink water

It doesn’t matter whether your flow is light or above average — you’re still losing fluid. Staying hydrated can help ease, and may prevent, symptoms like nausea and dizziness.

Eat iron-rich foods

Heavy blood loss can lead to iron deficiency, which may leave you feeling tired and lethargic. To help restore your levels and ease symptoms before and during your period, try eating iron-rich foods such as:

  • eggs
  • meat
  • fish
  • tofu
  • nuts
  • seeds
  • whole grains

Periods can change from month to month. Your period might be heavy one month and light the next for no other reason than that’s the way your body works.

If you’re experiencing new symptoms or think your period if unusually heavy, see your doctor. If nothing else, your doctor can reassure you that your period is indeed normal.

If they do suspect an underlying cause, they’ll work with you to diagnose your symptoms and develop a treatment plan tailored to your needs.