Free tool · educational, not diagnostic
Blood volume calculator.
How many litres of blood does a human body hold? Enter a body weight and see the estimate, plus what one standard donation really takes.
Adults roughly carry about 70 mL of blood per kg of body weight; children slightly more per kg.
Why the donation number matters
A standard voluntary donation in India is about 450 mL of whole blood. For a typical adult that is well under a tenth of total volume, your body replaces the plasma within about a day and the red cells within weeks. That is why donating is safe for healthy people, and why the rest periods (3 months for men, 4 months for women) exist: they give red-cell levels time to fully recover.
Full detail: How much blood does a human have? · Ready to be that fraction for someone? Register as a donor.
Where the numbers come from
A standard estimate: about 70 mL of blood per kg of body weight. A 60 kg adult carries roughly 4.2 litres; an 80 kg adult about 5.6 litres. It is an estimate, exact volume varies with build and sex, but it is the figure used in physiology teaching.
The part that matters to donors
A donation takes a fixed 350 mL in India (about 8% of most adults' blood). Your body replaces the fluid within a day or two and the red cells over weeks, which is why the gap is 3 months for men and 4 for women. Full breakdown here.
Related: iron and donation · after you donate.