Science
The human body
How the body is built and how it works, from cells and organs to the senses, measured in plain numbers.
Fact files
All topics ›The stomach
1 to 2 pH
Acidity of the stomach lumen
The small intestine
3.05 metres
Length in a living person
The human microbiome
38 trillion
Bacteria in a 70 kg reference man, 2016 estimate
The human heart
about 100,000 beats
Heartbeats per day, on average
Human skin
1.5 to 2.0 square metres
Average adult skin surface area
The human skeleton
206 bones
Adult skeleton, the usual count (some sources give up to 213)
The human eye
120 million rods
Rod photoreceptors in the human retina, about
The human brain
86 billion neurons
Nerve cells in the human brain, about
Human blood
5 litres
Blood in an average adult man (about 4 litres in a woman)
Human DNA
3 billion base pairs
Size of the human genome, about (one source gives 3.2 billion)
