How much do we bleed during our period? My absurd journey through the world of menstrual research

Many sources claim that people with periods bleed between 30 and 40 ml (3-5 teaspoons) on average during their menstruation. 60 ml is considered a heavy flow and if you are +80 ml, you are advised to see a doctor.

I went to see a doctor, because I honestly started worrying: I empty at least four full Ruby Cups during my period! A Ruby Cup Medium can hold 24ml which equals 4x of what a tampon can hold. So my flow is around 100 ml. I went to see my doctor to check with her about my heavy flow, since I actually felt that everything was fine, and luckily she confirmed that I have no cysts, no uterine fibroids, no endometriosis and no thyroid problems.

A little curious, I asked my friends about their experiences and what they told me was similar: those who use menstrual cups mentioned that they had at least 3 full cups during the first days. So again, a minimum of 80 to 120 ml of blood loss during their period was the most common quantity. So how come we, according to some research, should go see a doctor because of excessive flow? This seemed weird to me. Heavy periods can of course be an emotional burden for some and if your heavy period is intervening with your daily life, it’s definitely a sign to go see a doctor. You should not have to suffer and there are solutions. But that’s the point: none of us seemed to be suffering from our apparently  “excessive periods”. And so I began my research.

Diving into the menstrual research

Confirming the basics

First, I investigated the numbers. Websites like Wikipedia report the same as scientific publications on the topic (1, 2, 3). They all agree that 30 to 50 ml of blood loss during a period is the norm. Only one article from 1998 (4) has a slightly different opinion, stating that “too heavy periods” start at +120ml (and not +80ml).
So what is going on here? How come the difference is so significant between my friends’ perception and mine and the scientific sources about menstrual blood loss? I put on my detective hat and dove even deeper into the bloody subject.

The equation that calculates menstrual blood loss

I made an incredible discovery: I found an equation (5). A statistical equation to calculate menstrual blood loss, can you imagine!? I studied statistics and I know about the thrill of finding a great equation with precise estimations but an equation for menstrual blood loss? Isn’t this a very complicated way to assess something really easily measurable with a menstrual cup?

The equation is based on women keeping a diary and focuses on the following factors:

  • The number of days when “heavy”, “normal” and “light” bleeding is experienced
  • Spotting
  • the haemoglobin and serum ferritin values
  • as well as age.

Equation to calculate menstrual blood loss-min

The hands-on method that involves used tampons and pads

Later on, I discovered that this model was computed to facilitate another method called the Alkaline-Haematin-Method, which is the most commonly used method for estimating menstrual blood loss. I thought: If the first equation was to facilitate the Alkaline-Haematin-Method, how complicated can this method be?

Reading on, it turned out to be complicated and very old.  The Alkaline-Haematin-Method was established in 1964 (6) but is still referred to as “the current standard for quantification of menstrual blood loss” (5). It’s from the 60s, imagine – as if we were all still using corded phones and impatiently waiting for the next Beatles album to come out on vinyl.  Mind you, we’re currently at the stage of self-driving cars…just imagine if we invested the same amount of effort into understanding menstruation in all its facets.

However, I also thought, if it’s still used today, there must be something to it, right? I am not a chemist but as far as I understand, the Alkaline-Haematin-Method was developed as follows: To arrive at the estimated blood loss, they collected used disposable pads and tampons from menstruators. The collected products were then brought to a laboratory, where they were washed with a chemical liquid that reacts with the old, dried blood. The result of the chemical reaction is a substance called alkaline haematin (hence the method’s name).

Mind you, we’re currently at the stage of self-driving cars…just imagine if we invested the same amount of effort into understanding menstruation in all its facets.

But…what about menstrual cups?

Methods and data on how alkaline haematin yields the quantity of blood already exist in the scientific community. So, that’s how researchers achieved the results. I was really surprised. As a menstrual cup user, I thought: How come no new method has emerged since then instead of this seemingly complicated method? (I feel the urge to again mention that we currently have self-driving cars available but we have to collect used tampons to calculate menstrual blood loss…)

Using menstrual cups just seems so much easier to me than all these mathematical equations and chemical reactions. I tried to find information about using menstrual cups as a method, but I only found vague sources, where a menstrual cup or something similar to it (called the Gynaeseal) was deemed “unsuitable as a diagnostic tool for the quantification of menstrual blood loss” (3). The justifications were that these devices were not suitable for heavy bleeders and have a generally low acceptability rate within society based on articles from the 90s (7, 8). But with a clear increase in happy menstrual cup users across the world as well the availability of cups with a higher capacity than the Gynaeseal (a Ruby Cup medium can hold up to 4x more than a tampon), this argument is outdated.

So – what now? At this point in time, I was mostly just confused. Strange images stuck in my head with research assistants washing disposable menstrual products while writing complicated equations on a board.

I hadn’t come any further in finding an answer to my initial question: How come there is such a huge difference between my personal period experience and the sources claiming a blood loss of 80 – 120 ml as “risky”, “abnormal”, and “see a doctor”-like?

The answer lies in the details: menstrual blood vs menstrual fluid

I couldn’t get the 30 to 50 ml of blood loss on average, equations and pad-washing as means to get to this result out of my head. I had to check the Alkaline-Haematin-Method again and discovered that I had missed a crucial detail: What if the method is only considering the quantity of menstrual blood and not all of the menstrual fluid?

Those menstruating may have realized that what menstrual cups, pads or actually any menstrual product  collect isn’t just blood.  Actually, blood only makes up 36% of the menstrual flow! (9) Period flow is not as simple as a nosebleed.

So of course, the menstrual flow is made up of blood and other substances (3), the other substances being uterine lining and other tissue, no wonder a menstrual cup fills up faster and my experience far from the 30-50 ml norm. Just imagine a small shot glass of water and adding pebbles. It’s physics!

Going forward from this theory, I made a very basic calculation with the NHS number of 40 ml of average blood loss during a period and came to a result of 111 ml of total menstrual fluid lost during a period. Here’s how I calculated that:

At first, I was relieved. This corresponded perfectly well with my own measurements, so everything seemed fine and I had possibly found an answer to my initial question.

But this journey of discovery also made me think: Why are the scientific sources not more specific about this crucial information, as I’m almost certain I’m not alone in being confused by this whole blood vs flow issue.

Just a note as simple as: “the average quantity of menstrual blood loss during a period is 30-50 ml but if you take the entire menstrual flow into account, the average range is 100-120 ml. Flow consists of XYZ substances other than blood.” No biggie.

I got really worried by this missing clarification and I don’t think I’m the only one getting worried when scientific sources tell you that measuring ‘3 to 5 teaspoons’ of blood during your period is the norm.

Just to be clear, I’m aware of the risk of Menorrhagia (heavy menstrual bleeding)  and it’s crucial that menstruators facing this challenge receive help and find solutions on how to manage it. But maybe it’s time to update and nuance the information available on heavy periods.

Quantifying it at a level of +80 ml of menstrual blood loss possibly means making a lot of menstruators unnecessarily worried or scared. Hallberg and his team even found out that 40 % of women with a blood loss of +80 ml considered their menstruation “moderate” or “small” (2) – so why not follow this track?

Why we need to update & demand more menstrual research

Now, has my research led me to the right conclusion? I can’t be sure of that but according to the published research that I found, I will draw some further thoughts and questions from my adventure here:

Does the indicated norm of blood loss (3-5 tablespoons) by e.g. NHS take into account all the menstrual fluid or does it refer only to the quantity of blood?

If, technically speaking, the 30-50ml norm is the standard for an unproblematic period, then the problem is not the quantity but the fact that the terms used are misleading: it’s not 30-50ml of menstrual flow, it’s 30-50 ml of menstrual blood. As you could see in my calculations above, 40ml of menstrual blood corresponds to about 111ml of menstrual flow (blood clots, endometrial tissue, cervical mucus, etc. – the whole package).

This means we definitely have to be more accurate about the words we use – it’s very important that heavy bleeders facing health risks get help – that should be put at the forefront of it all. But it is also important not to scare people unnecessarily  – how can we improve the information to be more helpful and inclusive of all kinds of period experiences and as nuanced as possible?

Periods have been stigmatized and mystified in our society for so long – just think about the decades that ads made periods a blue, sterile, homogenous liquid free from blood clots. This mystification and taboo that surrounds periods have certainly not contributed to inclusivity and nuanced information about the menstrual fluid and periods in general – we need much more research and clarity.

This mystification and taboo that surrounds periods have certainly not contributed to inclusivity and nuanced information about the menstrual fluid and periods in general – we need much more research and clarity.

Periods vary from person to person and sometimes also from cycle to cycle. They vary in terms of colour and consistency – light red to dark brown, thin to thick or even blob like consistency.

That’s also why we have to be careful when using the words “risky” or “abnormal” for measuring period flow – what is “normal” for one person, does not have to be normal for another.

Also, what if our diets and lifestyle have taken its toll on the “period norm” during the past decades? A heavy period in the 60s is not necessarily the same today?

So, time for an update!

Update the knowledge available to us about periods, not least the medical professionals so they can advice accordingly – and to do that, we need to first be able to discuss menstrual flow without any judgement.

And I hope updating will also include the science. The fact that data on menstrual blood loss is based on methods from the 60s really stresses the need for more recent methodologies and data.  Maybe it’s time for a new menstrual blood/flow loss collection technique with a – wink-wink – menstrual cup.


  1. Dasharathy S., Mumford S., Pollack A., Perkins N. ,Mattison D., Wactawski-Wende J., Schisterman E. Menstrual Bleeding Patterns Among Regularly Menstruating Women. American Journal of Epidemiology. 2012;175(6):536-545.
  2. Hallberg L., Hôgdahl A., Nilsson L., Rybo G. Menstrual Blood Loss–A Population Study: Variation at different ages and attempts to define normality. Acta Obstetricia et Gynecologica Scandinavica. 1966; 45(3): 320-351.
  3. The Menorrhagia Research Group, Warrilow G., Kirkham C., Ismail K., Wyatt K. , Dimmock P. and O’Brien S. Quantification of menstrual blood loss. The Obstetrician & Gynaecologist. 2004; 6: 88–92.
  4. Janssen C., Scholten P., Heintz A. Reconsidering menorrhagia in gynaecological practice. Is a 30-year-old definition still valid? European Journal of Obstetrics, Gynecology, and Reproductive Biology. 1998; 78(1): 69–72.
  5. Schumacher U., Schumacher J., Mellinger U., Gerlinger C. , Wienke A., Endrikat J. Estimation of menstrual blood loss volume based on menstrual diary and laboratory data. BMC Women’s Health. 2012; 12(24).
  6. Hallberg L., Nilsson L. Determination of menstrual blood loss. Scand J Clin Lab Invest. 1964; 16(2): 244-248.
  7. Cheng M., Kung R., Hannah M., Wilansky D., Shime J. Menses cup evaluation study. Fertil Steril. 1995; 64(3): 661-663.
  8. Gleeson N., Devitt M., Buggy F., Bonnar J. Menstrual Blood Loss Measurement with Gynaeseal. Aust N Z J Obstet Gynaecol. 1993; 33: 79-80.
  9. Fraser I., MaCarron G., Markham R.,  Resta T. Blood and total fluid content of menstrual discharge. Obstet Gynecol. 1985; 65: 194–198.


Sarah Gorenflos (25) studied sociology and statistics in Konstanz and Vienna. During her studies, she worked as a research assistant at the chair of empirical social research with a focus on survey research. She is currently doing an internship at the Ruby Cup office in Barcelona.

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