Let it bleed

Do you remember that pinprick in your finger when a tiny bright red drop of blood surfaced on your skin? You were shocked, scared, almost panicked! You’re bloody well right. Bleeding is a risky business!

I remember a time in Surinam when we were walking in a swamp. Thousands of mosquitoes attacked us in such a vicuous way, each getting away with a tiny bit of blood, that we started to get visions, or rather nightmares, of acute anemia.

Every drop of blood is precious. But how many of these precious drops do we have in our body?

To know how many drops can be squeezed out of our finger tips, we have to know two things: How many liters of blood do we have in our body? and: How big is a drop?

Let it bleed Rolling Stones


As usual it takes some googling to get the simple answers, and some advanced math to get to the bloody truth.

How much blood in an average person?

Wikipedia says that “a typical adult has a blood volume of approximately between 4.7 and 5 liters, with females generally having less blood volume than males”. I am not a typical adult myself, but I will still use this 4.7 liters of blood as a starting point for my calculations.

It’s quite impressive, 4.7 liters. It’s a small bucket full of blood. Equivalent to almost 7 bottles of wine (red wine of course). But if you want to fill an Olympic-size swimming pool, you will need the blood of over half a million people.

How big is a drop of blood?

Not an easy question. In wiki.answers (usually not a very helpful source of information) I found that “an average size drop is about 50 ul”. The unit 1 ul is actually 1 microliter, which means 1 millionth of a liter. If you want to visualize it, it’s 1 cubic millimeter. So an average size drop of blood would be about 50 ul, which is 50 cubic millimeters.

If that is correct, a spherical drop of blood would have a diameter of 4.57 mm, which seems about right, except that drops are not really spherical. So I accept this figure and we will calculate with drop size of blood is 50 ul.


So how many drops of blood do we have?

With the above assumptions of 4.7 liters of blood in an average person and a blood drop size of 50 ul we can easily calculate how many drops of blood are circulating in that average person.

4.7 liters of blood is 4,700,000 microliters. So there are 4,700,000 divided by 50 drops in the person, which is 94,000 drops of blood (a person with 5 liters of blood has exactly 100,000 drops to spare).

So that pinprick was not that serious after all; you still have 93,999 drops left. But what about these mosquitoes? How much blood does a mosquito take in one bite?

Again, it was difficult to find this figure. On www.mosquitoworld.net I found that, depending to the species a mosquit can drink between 0.001 and 0.01 milliliters. So that would be between 1 ul and 10 ul. So even that biggest mosquito takes only one fifth of a drop. It takes 50,000 mosquito bites (50 kilobites) to take half a liter, which is what the blood bank usually takes. So if you get 1 mosquito bite per second, you should stay not more than 14 hours in that mosquito swamp.

More considerations

A spherical drop of blood with a volume of 50 ul has a diameter of 4.57 mm. An average person has 94,000 of these drops. If we put them all in a row, they would have a total length of 430 meters.

According to Wikipdia, the average distance from Earth to the Moon is 384,400 kilometers, which is 384,400,000 meters. So it takes less than 900,000 people to reach the moon with drops of blood. To reach Mars when it is close to the Earth (55,758,006 km on 27 August 2003) would require blood drops of almost 130 million people.

I’m bloody hungry now. So the story is finished.

By the way

Bloody well right is a song by Supertramp.

Let it bleed is a song by The Rolling Stones.