The average period produces about 60 milliliters of blood, which is roughly 4 tablespoons. That’s less than most people expect. The clinical threshold for heavy periods is 80 milliliters (just over 5 tablespoons), though what you see on your pad or tampon looks like far more than that because menstrual fluid isn’t pure blood.
What Menstrual Fluid Actually Contains
The fluid you see during your period is a mix of blood, tissue from the uterine lining, and other fluids. On average, blood makes up only about 36% of total menstrual discharge. The rest is mostly tissue fluid from the endometrium, with smaller contributions from cervical and vaginal secretions. This means if your total fluid loss over a period is, say, 120 milliliters, roughly 40 to 45 milliliters of that is actual blood.
The ratio stays fairly consistent regardless of how heavy your flow is or which day of your cycle you’re on. Women with heavier total fluid loss also have proportionally heavier blood loss, so the overall volume is still a reliable indicator of whether your bleeding is within a normal range.
How to Estimate Your Flow
Since no one measures their menstrual blood with a graduated cylinder, product capacity gives you a practical reference point. A 2024 study that tested modern menstrual products found the following blood capacities when fully soaked:
- Regular tampon: about 20 mL
- Heavy/super tampon: 31 to 34 mL
- Light day pad: about 4 mL
- Heavy day pad: 31 to 52 mL, depending on brand
These numbers represent fully saturated products. If you’re changing a regular tampon that’s only half soaked, you’re looking at closer to 10 mL per change. So a person using 6 to 8 regular tampons over a full period, none of them completely saturated, lands right around that 60 mL average. If you’re soaking through a heavy tampon every hour or two, you’re well above normal range.
When Bleeding Counts as Heavy
Clinically, heavy menstrual bleeding is defined as regularly losing more than 80 mL of blood per cycle. But the more practical definition, used by the UK’s National Institute for Health and Care Excellence, focuses on impact: heavy menstrual bleeding is excessive loss that interferes with your physical, emotional, social, or material quality of life. If your period is disrupting your daily activities, that matters regardless of the exact milliliter count.
Some concrete signs that your bleeding may be excessive:
- Clot size: Passing blood clots the size of a quarter or larger, according to the CDC.
- Product use: Needing to change a pad or tampon every hour for several consecutive hours.
- Double protection: Regularly needing both a pad and a tampon at the same time.
- Night disruption: Waking up to change products overnight.
The Iron Cost of Monthly Bleeding
Every milliliter of blood contains iron, and your period is the primary way premenopausal women lose it. A typical cycle costs about 1 mg of iron. That sounds tiny, but your body only absorbs 1 to 2 mg of iron per day from food, so menstrual losses eat up a significant portion of your daily iron budget.
Women with heavy periods lose far more. In one study, the median iron loss for women with heavy bleeding was 5.2 mg per cycle, roughly five to six times the normal amount. Over months and years, this creates a deficit that dietary intake alone can’t cover. In research comparing the two groups, women with heavy periods had notably lower iron stores. Among women of reproductive age overall, about 17% had ferritin levels below 7 ng/mL, a marker of depleted iron reserves. Fatigue, brain fog, and shortness of breath with exertion are common symptoms of this kind of slow iron drain, and they’re often attributed to other causes before anyone checks iron levels.
What Can Change Your Flow
Several factors shift your baseline in either direction. Hormonal contraceptives like the pill or hormonal IUDs typically reduce menstrual blood loss, sometimes dramatically. Some people on hormonal IUDs stop bleeding altogether.
Copper IUDs push flow in the opposite direction. In studies, women using copper IUDs saw their average blood loss rise from about 36 mL to 54 mL in the first few cycles after insertion, roughly a 50% increase. For women who already had heavy periods before insertion, the copper IUD bumped their average from 97 mL to about 107 mL. The increase tends to be most noticeable in the first two periods and then partially settles, though flow generally remains higher than pre-insertion levels.
Fibroids, polyps, and adenomyosis are structural causes of heavier bleeding. Thyroid disorders and bleeding conditions can also increase flow. Age plays a role too: periods often get heavier in your late 30s and 40s as you approach perimenopause, partly due to more frequent cycles without ovulation, which leads to thicker uterine lining buildup.
Tracking Your Period Objectively
If you’re trying to figure out whether your flow is genuinely heavy or just feels that way, a simple tracking method can help. The Pictorial Blood Loss Assessment Chart, or PBAC, is a tool originally developed in 1990 that assigns point values based on how soaked your pads or tampons are each day. Lightly stained products score 1 point, moderately soaked ones score 5, and fully saturated products score 10 to 20 points. You add up the total over your entire period.
A score of 100 or higher on the original chart was considered indicative of heavy bleeding, with about 86% sensitivity and 89% specificity. Later versions of the chart, calibrated to different product brands, have used thresholds ranging from 50 to 185. The exact cutoff matters less than the trend: if you track a few cycles and your scores are consistently climbing or consistently high, that’s useful information to bring to a healthcare provider. It turns a vague complaint of “my periods are really heavy” into something measurable.