Period Facts: How to Track your Menstrual Flow

We all talk to our closest friends and confidants about the pain and discomfort we experience during our periods. But the topic of blood loss rarely comes up. We know that our flow varies from day to day, but do we actually know how much blood and menstrual fluid we lose during our cycle? When is a period considered to be heavy?

Let's find out!

What is the menstrual flow?

Your menstrual flow is a cocktail of blood, endometrial-tissue fluid, cervical mucus, vaginal secretions and water. A direct-collection study in which volunteers emptied a menstrual cup into a graduated cylinder found an average total flow of 86 ± 48 mL per cycle (range 15 – 271 mL).

How much of that is blood 🩸?

That question goes to you: On average, how much blood is lost during a 28-day cycle?

an espresso ☕️ (30ml)
a soda can 🥤(255ml)
a bottle of wine 🍷 (750ml)

If your answer is a - (30 mL) or about 2 - 3 tablespoons of blood, then you are correct! Most research puts the average menstrual blood loss to around 33 mL. But it typically ranges from 10 to 35 mL. Anything more than 80 mL of blood or a flow lasting longer than seven days is labeled heavy menstrual bleeding (HMB).

A classic pad-weighing experiment showed the blood fraction averages 36 % of the fluid (but can swing from 2 % to 82 % between individuals).
When researchers measured blood and fluid side-by-side in heavier periods, they found blood accounted for 48 % of the flow when losses exceeded 60 mL and 50 % when blood loss topped 100 mL.

Bottom line: The headline 30–40 mL refers only to blood. Your total menstrual discharge is closer to 50–90 mL for an average cycle.

Why even bother to measure 🤷🏻♀️ ?

HMB affects up to one in five menstruators and is linked to anemia, missed work, and lower quality of life. Guidelines from the American College of Obstetricians and Gynecologists 👩🏻⚕️urge anyone with suspected HMB to track their loss before treatment decisions are made. If you know how much fluid your menstrual underwear can hold, you can translate it into the amount of liquid you lose. That gives you solid evidence for your clinician.

Three practical ways to estimate your flow 🛁

1. Count your products 🧺

Tampons: Light ≈ 5 mL, Regular ≈ 8 mL, Super ≈ 12 mL.
Pads: Daytime ≈ 5 mL, Overnight ≈ 10–15 mL.
Keep a simple tally on your phone and multiply by the corresponding milliliters.
Menstrual cup: Depending on the size, it could range from 10-30 mL. Check the brand of your menstrual cup to get the most accurate numbers and estimate from there.

2. Try a PBAC score 🗓️

Download a free Pictorial Blood Assessment Chart and give each lightly, moderately, or fully-soaked pad/tampon a point value; a monthly score > 100 usually means >80 mL of blood.

3. Use absorbency-rated period underwear 🩲

Relief-Wear’s Cotton Bikini is labeled “Light – 1 tampon,” roughly 5 mL (one regular tampon). Because the capacity is stated up front, every pair you saturate becomes a mini-measuring cup.

To estimate how much of your total flow is blood, multiply the volume by roughly 0.4 for light to average periods and by 0.5 when bleeding is heavy.

Red Flags 🆘 - When to go to the experts

Soaking a pad, tampon, or period underwear every hour for two hours straight ❗️
Bleeding > 7 days or passing clots > 2.5 cm
Total monthly volume over 80 mL by any method 🧻
Symptoms of iron deficiency: extreme fatigue, shortness of breath, pale skin

A sustainable tool that doubles as a tracker 📋

Switching to Relief-Wear leak-proof underwear cuts single-use waste and tells you, at a glance, how much you’ve bled. Heavy-flow styles hold three regular tampons’ worth, while lighter styles are perfect for spotting or cup back-up days. Because the gusset is charcoal-gray, you see saturation clearly, no guessing. Start logging how many pairs you fully soak each cycle. Every data point is a step toward better body literacy and lighter menstrual footprint.

Conclusion

The average period amounts to only a few tablespoons of blood, but everybody is different. By translating pads, tampons, or period underwear into milliliters—and supporting your iron stores, you’ll know when your flow is healthy, when it’s heavy, and when it’s time to seek extra help.