Period Blood Clot & Heavy Period Calculator
Track your clot size, pad and tampon changes, and flow across your period to get a validated blood-loss score — and see clearly whether your bleeding is light, normal, or heavy enough to check with a doctor.
Passing some clots on your heaviest days is normal. This tool gives you an objective score to describe your flow — useful for spotting heavy bleeding and for talking to your doctor — but it can’t diagnose a cause. If bleeding worries you, please see a healthcare provider.
Count everything across your whole period (all days combined). Not sure of exact numbers? A close estimate still gives a useful score.
Blood clots
Pads used (total for the period)
Tampons used (total for the period)
A few more details
Any of these alongside your period? (optional, tap any)
Fill in what you can above, then calculate to see your flow score and what it means.
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Where your score sits
About your clots
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What made up your score
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What to do next
This score is a screening aid, not a diagnosis. It estimates flow using the validated PBAC method, but products, habits, and bodies vary, so treat it as a guide. It can’t tell you why a period is heavy. Please see a healthcare provider if your periods are heavy, changing, or worrying you — and seek urgent care for very heavy bleeding with dizziness, fainting, or a racing heart.
How the period blood clot & heavy period calculator works
Passing clots is your body’s normal response to a heavy flow: when blood pools faster than your natural anticoagulants can thin it, it gels into clots. A few small clots on your heaviest days are usually nothing to worry about. What matters more is the overall picture — clot size, how often you’re changing pads or tampons, and whether you’re flooding. This calculator turns all of that into a single objective number using the Pictorial Blood Loss Assessment Chart (PBAC), a scoring method validated in clinical research and used to screen for heavy menstrual bleeding.
You count what you used across the whole period, rate how soaked each pad or tampon was, and note your clots. The tool adds it up, compares your score to the clinical heavy-bleeding threshold, estimates your blood loss, and tells you plainly whether it’s light, normal, heavy, or very heavy. If you’d also like to track flow volume day by day, pair it with our Menstrual Flow Volume Tracker.
Quick answer
Clots smaller than a coin (under 1 cm) are generally normal. Clots bigger than a quarter (over ~2.5 cm), or clots with a very heavy flow — soaking a pad or tampon every hour, or bleeding over 7 days — are worth discussing with a doctor. A PBAC flow score of 100 or more (roughly 80 mL of blood loss) is the recognised marker of a heavy period.
What clot size means
| Clot size | Everyday comparison | What it usually means |
|---|---|---|
| Under 1 cm | Pea to dime | Normal, especially on heavy days |
| About 2.5 cm | A quarter / coin | Upper edge of normal — worth watching |
| Larger than 2.5 cm | Grape to golf ball | Worth checking with a doctor, especially if frequent |
| Palm-sized or bigger | Golf ball to palm | See a provider; if you could be pregnant, seek care promptly |
When is a period considered “heavy”?
Clinically, heavy menstrual bleeding (menorrhagia) means losing more than about 80 mL of blood per cycle, or bleeding for more than 7 days. In everyday terms, the practical signs are soaking through a pad or tampon every hour for several hours, needing to double up on protection, waking overnight to change, passing clots bigger than a quarter, or feeling drained and breathless. Heavy periods are common — roughly a third of people who menstruate deal with them — and they’re very treatable, so they’re worth raising rather than putting up with.
Why heavy clots and flow happen
Most of the time it’s simply the natural coagulation process working overtime on a heavy day. But persistently heavy periods or large clots can point to something treatable, such as a hormonal imbalance, uterine fibroids, endometriosis, polyps, a thyroid issue, or a bleeding disorder. Heavy bleeding can also lead to iron-deficiency anemia, which is why tiredness, breathlessness, and looking pale are worth mentioning. Tracking your cycle first — including flow and clots — gives your provider useful information. Our Basal Body Temperature Charting Tool can help you spot broader cycle patterns.
A worked example
Say over one period you use 5 moderately soiled pads, 8 fully soaked pads, 6 soaked tampons, pass 4 small clots and 5 large clots, and flood twice. That scores around 284 — well above the 100 heavy-bleeding threshold, suggesting a very heavy period worth discussing with a provider. By contrast, 8 lightly stained pads, 4 moderately soiled pads, and one small clot scores about 29, comfortably in the normal range.
Related maternal health calculators
This tool is part of the Maternal Health Calculators hub. These companion tools cover cycle tracking, ultrasound dating, and pregnancy planning — each answers a different question, so choose whichever fits where you are.
Frequently asked questions
Yes, small clots are a normal part of menstruation, especially on your heaviest days. They form when blood pools faster than your body can thin it. Clots become worth checking when they’re larger than a quarter or come with a very heavy flow.
Clots smaller than a coin (under 1 cm) are usually fine. Clots bigger than a quarter (about 2.5 cm), or grape-sized and larger, are worth mentioning to a doctor — particularly if they happen often or with heavy bleeding.
Signs of a heavy period include soaking a pad or tampon every hour for several hours, doubling up on protection, waking to change overnight, passing large clots, bleeding over 7 days, or feeling tired and breathless. A PBAC score of 100 or more also indicates heavy bleeding.
The Pictorial Blood Loss Assessment Chart is a validated way to estimate menstrual blood loss. Each pad, tampon, and clot is given points based on saturation and size, then totalled. A score of 100 or more corresponds to roughly 80 mL of blood loss — the threshold for a heavy period.
A typical period is about 30–40 mL (a few tablespoons) across the whole cycle. Losing more than around 80 mL is considered heavy. Because measuring exactly is impractical, tools like this one estimate it from your pad, tampon, and clot counts.
Large clots usually accompany heavy flow, but can be linked to hormonal changes, uterine fibroids, endometriosis, polyps, thyroid issues, or a bleeding disorder. If large clots are new, frequent, or come with other symptoms, a provider can find out why.
Yes. Losing a lot of blood each month can lower your iron and lead to iron-deficiency anemia, which brings tiredness, breathlessness, and pallor. A simple blood test checks for it, and it’s very treatable, so it’s worth raising with your provider.
If you could be pregnant and are passing clots with bleeding, contact a provider promptly, as it can be a sign of early pregnancy loss. This calculator is for menstrual periods and isn’t designed to assess bleeding in pregnancy.
It uses the validated PBAC scoring system, which correlates well with actual blood loss and is used in research and clinics. Still, it’s a screening estimate, not a lab measurement or diagnosis. Your provider interprets it alongside your history and any tests.
See a provider if you regularly soak through protection hourly, pass clots bigger than a quarter, bleed over 7 days, feel drained or breathless, or your periods suddenly change. Seek urgent care for very heavy bleeding with dizziness, fainting, or a racing heart.
Methodology
This calculator uses the Pictorial Blood Loss Assessment Chart (PBAC), originally developed by Higham and colleagues and validated against the alkaline hematin reference method. Each item is scored: lightly stained pads 1 point, moderately soiled 5, fully soaked 20; lightly stained tampons 1, moderately soiled 5, fully soaked 10; small clots (under about 1 cm) 1 point each and large clots (over about 1 cm) 5 points each; and each flooding episode 5 points. The totals are summed across the whole period. A total of 100 or more is the conventional threshold for heavy menstrual bleeding, corresponding to roughly 80 mL of blood loss; some studies use a higher cut-off of 150 for greater specificity. Estimated blood loss is approximated from the score for context only. The symptom checklist highlights features associated with heavy bleeding and possible anemia. All results are screening estimates for education, not a diagnosis, and are not a substitute for assessment by a qualified provider.
Reviewer
References & trusted sources
- Quantifying Menorrhagia & the PBAC (NCBI / PMC review)
- ACOG — Heavy Menstrual Bleeding (FAQ)
- Mayo Clinic — Blood clots during menstruation
- NHS — Heavy periods
Last reviewed & updated: July 2026.