There are a couple of reasons why men have a higher blood volume than women, and here are some of them:
1. they are taller - given that usually male bodies are larger than those of women, they need more blood to flow through such a vast vessel
2. men have testosterone - this hormone increases the production of erythrocytes, or red blood cells
3. women menstruate - during this period of month, women lose a portion of the blood, which is why they have less