Menstrual blood loss… What’s normal?

Here is our myth-busting guide to help you know the difference between ‘normal’ and problematic ‘heavy’ menstrual flow, estimate your own fluid/ blood loss, and find out which underlying conditions can cause Heavy Menstrual Bleeding (HMB).


1. How much blood/ fluid loss is ‘normal’?

Double espresso cup with coffee beans

Photo by Dominika Roseclay from Pexels

First off, you need to know something that you were probably never taught at school (even medical school!)- Which is that only approx. 50% of menstrual fluid is blood [1].

On average, people who menstruate lose ~ 70-80 ml of fluid (~ 35-40 ml of blood [1]) per period [2]. This amount of fluid would fill a double espresso cup (image on left) [3].

Half full clear plastic cup

Photo by Meir Roth from Pexels

In fact, anything up to ~ 160-170 ml of fluid (~80 ml of blood) per period falls within the ‘normal’ range [2]. This is because ~ 95% of all people who menstruate typically lose less than this amount [2]. This total amount of fluid would fill a tall (7oz) disposible plastic cup (image on right) [4].

Notes– variation is the norm when it comes to menstrual health- it is important to track your cycle for a while to work out what is the ‘normal’ range of experiences for you. This will help you to spot any significant or unusual changes in the future. Hormonal contraceptive medication is known to significantly reduce cyclical fluid/ blood loss in those with no underlying health issue [5].

What’s not normal?

Technically speaking, Heavy Menstrual Bleeding (HMB) is losing over 80 ml blood (~ 160-170 ml of fluid) per period [2]. Most people with this condition lose between 80- 200 ml of blood (160-400 ml of fluid) per period, but some people can lose even more than this [2].

Heavy Menstrual Bleeding (HMB) can also make the period last longer than a ‘normal’ one [6]. Most people have periods that last between 3-7 days, with at least 80% of the total fluid/blood loss happening on days 1-3 [6]. If your period typically lasts longer than 7 days, especially with significant fluid/ blood loss over more than just the first 3 days, you may be experiencing HMB [6].

Left untreated, HMB rapidly results in iron deficiency anaemia, and the awful thing is, anaemia makes periods even heavier [7]… It’s a truly vicious cycle! It is therefore important for clinicians to simultaneously treat iron deficiency anaemia alongside any other investigations/ interventions for Heavy Menstrual Bleeding [7].

2. How do you measure menstrual blood/ fluid loss?

We can roughly calculate blood loss by simply halving the total fluid loss… So this really depends on the collection method you prefer to use.

Menstrual cups now provide the easiest and most accurate way to measure fluid levels, since many of them come with a handy scale on the inside [8]. Others may just list their total capacity size, which still enables users to estimate how much fluid has been collected over the course of a period. Simply look at how much fluid is in the cup when changing it and note it on your phone, or on paper. Do this throughout the whole period, since diagnostic cut off points are based on total blood loss per period.

Disposable items, such as pads and tampons all have to meet the same absorbency standards [9]. This means that it is possible to roughly estimate fluid loss by counting how many tampons or pads you bleed through during your period.

The chart below shows the exact standard ranges [10], which are actually based on weight, rather than fluid level- but this is still a good way to roughly calculate fluid loss. For example, each (fully soaked) regular soaked tampon or pad ~ 7ml, each ‘super’ ~ 10ml, each ‘super plus’ ~ 13ml, and each ‘ultra’ ~ 16ml.

The problem is that many people change their pads and tampons before they are fully soaked, so the accuracy of this method is reduced – although it is possible to use a visual ‘pictogram’ scale to estimate fluid loss [11]. People also tend to use products with different levels of absorbency throughout their period, so it is important to note down the exact type of product used.

Ranges of absorbency in gramsCorresponding term
6 and underLight
6 to 9Regular
9 to 12Super
12 to 15Super plus
15 to 18Ultra

Pants on a washing lineWashable items, such as period pants, or washable pads may make estimating fluid loss more difficult, because there is no universal standard of absorbency for these items (yet). However, if you are concerned that you may be experiencing heavy bleeding, it might be worth using a cup for a few cycles, just to help you and your doctor make a more informed decision about possible treatment options?

Another less accurate, but practical guide is noting the number of times you have to change your menstrual underwear, cup, pad or tampon in a given time period. If you can answer yes to any of the following questions, you could well be experiencing Heavy Menstrual Bleeding (HMB) [12];

  • Do you have to wear tampons/ cups and towels together to prevent leaking through clothing?
  • Do you have to change items more than once every 2 hours?
  • Does blood ever soak right through your clothes, even though you are using a menstrual product?
  • Do you have to stay off work or cancel social engagements due to heavy bleeding?

3. What causes Heavy Menstrual Bleeding?

Note– It is very important that you seek medical advice if you experience a significant change in your period flow, or any mid-cycle bleeding.

Heavy Menstrual Bleeding (HMB) can be caused by various, and sometimes multiple, factors [13]. Luckily for us, the possible causes are listed in a handy acronym- PALM-COEIN [13].

a female abdomen with the words 'out of order' written in marker pen

Photo by Kat Jayne from Pexels

The first group (PALM) relates to structural problems- it is thought that growths in or around the womb increase the surface area of the womb’s lining (increasing the amount of tissue/ blood loss) and/ or interfere with the normal constriction of muscle and blood vessels involved in stopping menstruation (i.e. prolonging the period) [14]. These growths are categorised as; Polyps, AdenomyosisLeiomyoma (aka fibroids!), and Malignancy (e.g. womb cancer). By far the most common of these causes are fibroids and polyps, then adenomyosis, and only very rarely, more serious issues such as womb cancer.

The second group (COEIN) relates to non-structural problems: Coagulopathy (i.e. blood clotting disorders- approx. 13% of HMB cases are caused by these e.g. Von Willebrand’s Disease [15]), Ovulatory Disorders (e.g. hormonal changes associated with the peri-menopause, Polycystic Ovary Syndrome, thyroid or pituitary gland disorders), Endometrium (e.g. a blood clotting issue found only in the lining of the womb- usually diagnosed after excluding all the other possibilities), Iatrogenic (non-biological chemical factors- e.g. cigarette smoking, the copper coil (IUD), hormonal contraception, anti-convulsant, antidepressant, or anti-psychotic medications, and antibiotics such as rifampin and griseofulvin) and, lastly, Not Yet Classified (other gynaecological issues may play a role in HMB but are difficult to identify- this category will develop as further research is conducted) [13].

Treatment options obviously vary according to the cause(s), but it is definitely worth taking iron supplements regardless, since iron-deficiency anaemia plays a large part in the life-affecting symptoms of HMB (i.e. fatigue) and can further increase menstrual blood loss [7].


A bonus note for clinicians/ menstrual health and rights enthusiasts;

question mark made out of medical pills

Photo by Anna Shvets from Pexels

A few years ago, it was decided to just trust that people who sought help from their doctor for very heavy periods, really did have them [16]. This is actually a very nice intention; a decision to believe in female patients rather than dismiss them as ‘prone to exaggeration’ (which is sadly still a common experience). Unfortunately, menstruation education is typically of poor quality and so people who menstruate often do not have an informed idea if their flow is average, heavy- or even heavy enough to be Heavy Menstrual Bleeding (HMB).

It has been argued that it is better to treat all of those who think they have this condition, rather than measuring fluid/ blood loss or otherwise making a diagnostic distinction (e.g. asking the screening questions listed above) [17]. However, I am concerned that by doing this we are actually reinforcing a sexist myth that positions all menstruating people as debilitated (the medicalisation of menstruation), as well as normalising the exceptionally severe experiences of those few who really do lose over 80 ml of blood per period (the minimisation of serious women’s health issues).

The impact – Clinical research on HMB has found that a significant proportion (sometimes the majority) of trial participants, actually have ‘normal’ menstrual flow, which obviously messes up the findings [18]. Plus, the prevalence of Heavy Menstrual Bleeding can become highly exaggerated: A highly-cited UK study [19] simply asked people about their typical menstrual flow and roughly equated the subjective categories ‘variable’, ‘heavy’ and ‘very heavy’ with the sort of experiences described by people with HMB. Unsurprisingly, it reported an extremely high prevalence rate of debilitating blood loss in the UK population- around 25% [19]! This is not good for science or for society.

With menstrual cups, we now have a much simpler way to measure fluid loss/ estimate blood loss and so I think it is probably best to stick to the 160 ml fluid/80 ml blood loss categorisation, when deciding how best to treat an individual patient. For example, it may be that someone who has normal flow but feels it is ‘too heavy’ simply requires some further information about blood loss, how to manage periods, or perhaps even specific medical treatment for a different health issue (e.g. iron deficiency anaemia). They certainly should not be incorrectly categorised as having a serious health condition such as Heavy Menstrual Bleeding. Likewise, those who do have this condition, urgently require specific tests and specialist medical support, and should not be categorised as merely falling at the far end of the ‘normal’ curve when it comes to menstrual blood loss.


Cite as: King, S (2020) ‘Menstrual blood loss… What’s normal?’ Menstrual Matters Blog accessed [date] https://www.menstrual-matters.com/blog/bloodloss/


References and Notes;

[1] ‘Menstrual fluid’ is not the same as ‘blood’, menstrual fluid also contains beautifully silky cervical mucous and vaginal secretions. A high quality study found that typically, approx. 48-50% of menstrual fluid is blood and that “if total fluid volume is measured carefully, the estimate of actual blood loss is sufficiently accurate for clinical purposes“- Fraser IS, Warner P, Marantos PA. (2001) ‘Estimating menstrual blood loss in women with normal and excessive menstrual fluid volume’. Obstet Gynecol. 98(5: 1):806-14. PubMed PMID: 11704173

[2] The study that first determined an average blood loss of 30-40 ml, and 80ml blood loss as the 95th percentile cut-off point, was Hallberg L, Höegdahl AM, Nilsson L, Rybo G (1966): Menstrual blood loss – a population study. Variation at different ages and attempts to define normality. Acta Obstet Gynecol Scand 45:320–351 These findings were replicated in subsequent studies e.g. Scambler, A., & Scambler, G. (1985). Menstrual symptoms, attitudes and consulting behaviour. Social Science and Medicine, 20(10), 1065–1068, and Shaw Jr ST, Aaronson DE, Moyer DL. (1972) Quantitation of menstrual blood loss–further evaluation of the alkaline hematin method. Contraception 1972;5(6):497–513, and many others listed below.

[3] Ah yes, the age-old quest to visualise the amount of fluid lost during a period… I’ve opted for drinking vessels, since these are much more commonly used than egg cups or tablespoons! A double espresso cup typically holds 80ml of super strength coffee… The same as the average amount of fluid lost during a period!

[4] Yep, this time I went for the good old plastic cup. While it is crap for the environment and likely a product of horrific labour abuses, it does make a decent visual aid for describing the maximum ‘normal’ fluid loss approx. 170 ml/ 7oz.

[5] Davies, J., & Kadir, R. A. (2017). Heavy menstrual bleeding: An update on management. Thrombosis Research, 151, S70–S77. doi:10.1016/s0049-3848(17)30072-5

[6] Magnay, J. L., O’Brien, S., Gerlinger, C., & Seitz, C. (2018). A systematic review of methods to measure menstrual blood loss. BMC women’s health18(1), 142. https://doi.org/10.1186/s12905-018-0627-8

[7] See Percy, L., Mansour, D., & Fraser, I. (2017). Iron deficiency and iron deficiency anaemia in women. Best Practice & Research Clinical Obstetrics & Gynaecology, 40, 55–67. doi:10.1016/j.bpobgyn.2016.09.007 and Taymor ML, Sturgis SH, Yahia C. (1964) The etiological role of chronic iron deficiency in production of menorrhagia. JAMA 187:323–27.

[8] A recent study found menstrual cups to be an effective way to measure fluid loss- Donoso M, B, Serra R, Rice G, E, Gana M, T, Rojas C, Khoury M, Arraztoa J, A, Monteiro L, J, Acuña S, Illanes S, E: (2019) Normality Ranges of Menstrual Fluid Volume During Reproductive Life Using Direct Quantification of Menses with Vaginal Cups. Gynecol Obstet Invest 84:390-395. doi: 10.1159/000496608

[9] Disposible product manufacturers were forced to standardise their absorbancy levels after Procter and Gamble’s ‘Rely’ tampon – Toxic Shock Syndrome scandal in the late 1970s (resulting in several deaths and thousands of infections)- see Vostral S. L. (2011). Rely and Toxic Shock Syndrome: a technological health crisis. The Yale journal of biology and medicine84(4), 447–459.

[10] The FDA menstrual product absorbancy standard is written in full here- https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?fr=801.430 

[11] For more information on the ‘pictogram’ method of estimating blood loss see; [5] [6] above or Quinn, S. D., & Higham, J. (2016). Outcome measures for heavy menstrual bleeding. Women’s health (London, England)12(1), 21–26. https://doi.org/10.2217/whe.15.85

[12] These are the questions advised by the NHS information standard on heavy menstrual bleeding- https://www.nhs.uk/conditions/heavy-periods/

[13] Munro, M., Critchley, H., & Fraser, I. (2011). The Flexible FIGO Classification Concept for Underlying Causes of Abnormal Uterine Bleeding. Seminars in Reproductive Medicine, 29(05), 391–399. doi:10.1055/s-0031-1287663

[14] Hapangama, D. K., & Bulmer, J. N. (2016). Pathophysiology of heavy menstrual bleeding. Women’s health (London, England)12(1), 3–13. https://doi.org/10.2217/whe.15.81

[15] Shankar M, Lee CA, Sabin CA, Economides DL, Kadir RA. (2004) von Willebrand disease in women with menorrhagia: a systematic review. BJOG. 111:734–740.

[16] NICE. Clinical Guideline 44; Heavy menstrual bleeding 2007. National Institute for Health and Clinical Excellence (NICE); Available at: http://www.nice.org.uk/nicemedia/pdf/CG44FullGuideline.pdf. [Ref list] [17] Warner PE, et al. (2004) Menorrhagia II: is the 80-mL blood loss criterion useful in management of complaint of menorrhagia? Am J Obstet Gynecol 190(5):1224–9.

[18] “The percentage of women with self-perceived HMB and a measured MBL of 80 mL or more was assessed in nine studies and found to range from 26 to 76%” – Magnay, J. L., O’Brien, S., Gerlinger, C., & Seitz, C. (2018). A systematic review of methods to measure menstrual blood loss. BMC women’s health18(1), 142. https://doi.org/10.1186/s12905-018-0627-8

[19] [Bad science alert!] Shapley, M., Jordan, K., & Croft, P. R. (2004). An epidemiological survey of symptoms of menstrual loss in the community. The British journal of general practice : the journal of the Royal College of General Practitioners54(502), 359–363.

Categories: anaemia, Fibroids, Heavy Menstrual Bleeding (HMB) and Myth busting.

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