The short answer
Pick your flow for each day of your period. The calculator adds up an estimate of the blood lost and turns it into iron, at about 0.5 mg of iron per mL of blood.
Your period, day by day
A typical period
Food puts back about 1 to 2 mg of iron a day, and everyday losses take about 1 mg. Even on good days that leaves you about 1 mg ahead, so this period takes at least 24 days of iron meals to replace.
An estimate from textbook averages, not a measurement.
How the estimate works
| Flow | Blood a day, estimate |
|---|---|
| Spotting | about 1 mL |
| Light | about 4 mL |
| Medium | about 8 mL |
| Heavy | about 14 mL |
Each day's flow is turned into millilitres from textbook averages, added up, and multiplied by 0.5, the milligrams of iron in a millilitre of blood. A typical period lands at 30 to 40 mL, about 15 to 20 mg of iron. Over 80 mL is the usual definition of a heavy period.
This is an estimate, not a measurement. Pads, tampons and cups hold different amounts, and everyone describes flow differently. Use the number to see the size of the loss and to compare months.
The Ferritin app does this sum for every period you log, and puts the iron on the same timeline as your blood tests. Read more about what a period costs.
Questions
Why do the numbers seem small?
A period feels like more blood than it is. 30 to 40 mL is about two to three tablespoons, spread over several days.
Can I measure my flow more exactly?
A menstrual cup with markings gives a closer number. Note the millilitres and compare them with the estimate here.
Sources
- 1.Hallberg L. et al. Menstrual blood loss: a population study. Acta Obstetricia et Gynecologica Scandinavica, 1966
- 2.NICE guideline NG88. Heavy menstrual bleeding: assessment and management
- 3.The Iron Guide, part 1: Why iron
This page has not been reviewed by a clinician yet. Read it as general education, and take your own results to your doctor.
Educational, not medical advice. ferritin.ai does not diagnose or treat any condition, and it never sets a dose. Talk to your doctor about your own results.