How heavy is heavy? Reading your own flow

On a box, “heavy” is the maker’s word. It does not say what it measures. For a period, the word works differently. The SOGC gives a clinical line in millilitres. Blood loss is hard to measure, though, so most health sources also describe heavy periods by a short list of signs. This Column puts those lists side by side, in the sources’ own words. It is for everyone who has periods, and for anyone who has wondered whether their own heavy days count.

Why a number doesn’t settle it

Start with volume, because it is the number people look for. The sources do not agree on what a usual period holds. The SOGC puts it at “around 2-3 tablespoons (30-50 mL)”. UBC’s Centre for Menstrual Cycle and Ovulation Research (CeMCOR) says: “The usual amount of blood loss per period is 10 to 35 ml.” The NHS gives a wider range again: “about 20 to 90ml”.

For heavy, the SOGC gives a clinical line: “Clinically, HMB (also called menorrhagia), is a loss of 80 mL of blood or more, in one cycle.” CeMCOR uses its own term for the same range. It says flow of more than 80 mL in a period “is considered very heavy flow”.

Each figure carries its source. The SOGC adds two cautions. In its words, “Measuring the amount of blood lost via menstruation is not that easy, since it is hard to tell how much blood has been absorbed by a pad or tampon.” It also says: “your perception of your bleeding is more important than the actual amount of blood loss.” That is one reason the sources rely on signs and counts, not millilitres.

The signs, in the sources’ words

The SOGC is the Canadian reference. It lists five signs of heavy menstrual bleeding. In its words:

• “Bleeding that lasts more than 7 days.”
• “Bleeding that soaks through one or more tampons or pads every hour for several hours in a row.”
• “Needing to wear more than one pad at a time to control menstrual flow.”
• “Needing to change pads or tampons during the night.”
• “Menstrual flow with blood clots that are as big as a quarter or larger.”

The NHS in the UK and the CDC in the US keep similar lists. The NHS adds changing “every 1 to 2 hours, or empty your menstrual cup more often than is recommended”, bleeding “through to your clothes or bedding”, and feeling “tired or short of breath a lot”. Its clot size is “about 2.5cm (the size of a 10p coin)”, a UK coin, where the SOGC uses a Canadian quarter. The CDC lists changing “after less than 2 hours” and being “tired, lack energy, or are short of breath”. The CDC estimates that “about 1 of every 5 women” in the United States has heavy menstrual bleeding. That is an American figure.

Night-time is on all three lists. The SOGC and the CDC name changing during the night, and the NHS names bleeding through to bedding. Sleeping on your period has its own Column.

A note on words: some sources we cite here say “women” or “females”. We keep researchers’ words so we report their findings accurately. The Reading Room is for everyone who menstruates.

Doubling up is on the list

On the heaviest days, some people wear two products at once: a period pad with a tampon, say, or two period pads. In online forums, some people describe this as an ordinary heavy day.

Three of the health sources quoted here list it as a sign of heavy bleeding. The SOGC says “Needing to wear more than one pad at a time to control menstrual flow”. The NHS says “need to use 2 types of period product together, such as a pad and a tampon”. The CDC says “Need to double up on pads to control your menstrual flow”.

The sources list doubling up among the signs of heavy menstrual bleeding. On its own it is not a test, and it cannot tell you what is happening in your body. The CDC’s advice for this kind of bleeding: “you should see a healthcare provider.”

Counting, if you want numbers

Some people like to bring numbers to an appointment. The sources offer a few ways to count. These are tools to take to a healthcare provider, not a test to score at home.

HealthLink BC describes heavy periods as “soaking 12 or more regular sanitary products in one period or soaking through a regular sanitary product every hour for several hours”. CeMCOR says the definition of heavy flow “can be adjusted to be nine to 12 soaked regular-sized sanitary products in a single menstrual period”. It adds that “flow of more than 80 ml (or 16 soaked normal-sized ‘sanitary products’) per whole menstrual period is considered very heavy flow”.

Notice the word “soaked”. In these counts, a half-used product is not a soaked one.

The SOGC also points to two tools: a “Pictorial Blood Assessment Chart” and the Self-BAT, a bleeding assessment questionnaire. The Glossary cards below explain both.

Iron, briefly

Iron often comes up beside heavy periods. The NHS mentions blood tests for “iron deficiency anaemia”. The NHS and the CDC both list tiredness or shortness of breath among their signs.

In Canada, researchers analysing the Canadian Health Measures Survey (2012–2019) estimated iron deficiency in 21.3% of females aged 14 to 18 and 18.2% of females aged 19 to 50. These figures are not adjusted for inflammation; the researchers’ adjusted estimates were higher. A second analysis of the survey (2009 to 2017, women aged 20 to 79) found iron deficiency in 16.0% of premenopausal and 4.0% of postmenopausal women.

These figures describe a population. They do not explain any one person’s iron. Questions about your own iron belong with a healthcare provider.

What each format offers on heavy days

What follows describes each format on heavy days, in the house’s fixed order. It is not a ranking. Two people with the same flow choose differently, and both are right.

Period pads & liners. Disposable period pads come in larger sizes and in versions labelled for heavy flow or overnight. Those words are each maker’s own. In Canada, no absorbency standard sits behind them. The maker’s package and instructions are the place to read what each size means.

Tampons. Tampons are the only format with Health Canada absorbency labels, from Light to Ultra. Health Canada says: “Use the lowest absorbency that will meet your needs.” It also says: “Change your tampon every 4 to 8 hours, and do not use tampons overnight.”

Cups. Cups collect period blood rather than absorb it. Cup makers state a capacity, often in millilitres. One Canadian maker’s guide says: “Depending on your menstrual flow, you may have to empty it more frequently.” The maker’s instructions set the wear time.

Discs. Discs also collect rather than absorb, with a capacity stated in millilitres. One Canadian maker’s instructions say to empty it at least every 12 hours; another maker describes up to 12 hours of wear. As with cups, the maker’s instructions set the wear time, and they are worth reading before a heavy day.

Period underwear. Period underwear is worn in place of regular underwear. Its absorbency is described in each maker’s own units, such as “tampons’ worth”. In Canada, no required standard test sits behind those units. The maker’s label says what each style is meant to hold.

Reusable period pads. Reusable period pads are washed and worn again. They come in sizes and absorbencies set by each maker. No Canadian absorbency standard was found for them. As with disposable period pads, the words on the label are the maker’s.

Comfort & care. Some people keep practical items for heavy days: a wet bag for carrying used reusables, or a mattress protector. These are household items, not treatments.

The SOGC says: “If you are struggling to cope with the amount of bleeding you are experiencing, see your doctor.” A bigger product can change how often you change it. It cannot tell you why the bleeding is heavy.

What this is not

This Column set out what named health sources say about heavy periods, and described each format on heavy days. It is not a test, and it cannot tell you whether your own periods are heavy. It did not compare brands or rank formats. It makes no claim that any product manages or treats heavy bleeding.