# What percentage of human body's cells are contained in blood?

What percentage of human body's cells are contained in blood vs. the rest of the body?

• The background of the question was a (somewhat silly) theoretical question of "how much of your body's cells can you replace with blood transfusion". I realize that the exact biological answers to the two questions will be different, but I think it's a good first approximation.
– DVK
Feb 23 '15 at 16:38
• You should probably edit the question to contain that background then. Feb 23 '15 at 16:38
• When you mean "percentage", do you mean my type or by mass? Feb 23 '15 at 20:06
• @anon by cell count
– DVK
Feb 23 '15 at 20:09
• According to this answer, there are 2.63 × 10^13 red blood cells, which is 70.69% of the 3.72 × 10^13 total human cells in the estimate. Jul 30 '15 at 4:25

The human body has about $3.72 × 10^{13}$ cells according to Bianconi et al. 2013, although this is disputed.

It also has about 5 liters of blood, which is made approximately 40-45% of erythrocytes. Let's assume 2.5 liters = 2500 $cm^3$ of red blood cells (RBC). Assuming a mean value of 5 millions RBC per $mm^3$ there should be in total $5 \cdot 10^6 \cdot 10^3 \cdot 2500 = 7.5 \cdot 10^{12}$ RBC.

By completely taking out white blood cells and thrombocytes out of the equation, a number of ${7.5 \over {3.72 \cdot 10}} \cdot 100 = 20 \%$ of number of cells are contained in the blood (approximately).

Given the hypothetical 70 kg man, let him be separated into components:

Blood: 7% (70 kg x .07 = 4.9 kg)

Of that, 60% is plasma, so (4.9 kg x .4 = 1.96 kg blood cell weight.)

Therefore of a 70 kg male, ~ 2 kg is blood cells

Tissue and bone: 93% of body weight (70 kg x .93 = 65kg)

Of that, 27% is extracellular fluid, so (65 kg x .73 = ~ 47.5 kg cell weight)

But we need to subtract the weight of bones:

Dry bone weight = ~6.5% total body weight, (70 kg x .065 = 4.55 kg bone weight)

So, cell weight minus extracellular fluid:

Blood cells: 2 kg Body cells (minus bone weight): 43 kg

2kg/(43kg + 2 kg) = 4.4% of the weight of cells in the body are the blood cells.

• Isn't a human being about 75% other organisms though? As in, of that 70kg, about 50kg doesn't actually have the human's DNA? Mar 11 '20 at 6:20