Liberal Arts Blog — Cells: How Big, How Long, How Many?

Liberal Arts Blog — Monday is the Joy of Math, Statistics, and Numbers Day

Today’s topic: Cells: how big, how long, how many

You can’t count them under a microscope. So how do you figure out how many cells there are in the human body? Well, you could figure out what the “average cell” weighs and go from there. Say the average cell weighs 1 nanogram and the average human weighs 70 kilograms, well then the average human has about 70 trillion cells! On the other hand, using average cell size of 1/40th of a millimeter you might end up with an estimate of 16 trillion. Over the last 100 years, estimates by scientists have ranged from numbers in the trillions to the quintillions. The consensus now is about 37 trillion of our own cells and 40 million alien bacterial cells. Experts — please chime in. Correct, elaborate, elucidate.


1. The female egg is actually “big enough to be just barely visible with the naked eye.”

2. The smallest? Sperm (without the flagellum). But is that the right metric? A sperm cell is about 30 micron cubed. 130,000 X smaller than the egg.

3. The reason for the egg’s huge size is all those nutrients in the cytoplasm.

NB: Sperm may be shrimps, but there are lots more of them. Women are born with about one million eggs, of which about 300,000 remain at puberty, and about 300 to 400 ovulated over a life time. A man produces about 3 billion sperms per month. 280 million per ejaculate.


1. A nerve cell can be up to 3 feet long!

2. But some are really short — less than a millimeter.

3. The ratio of the axon to the cell body of that 3 foot long neuron is something to think about. The cell body is usually about 100 microns in diameter. So imagine a 1.5 inch in diameter ping pong ball with a little tail attached. That tail would be 1287 feet long!

NB: the longest neuron in the body goes from the base of the spine to the big toe.

LONGEVITY OF CELLS: from days to a lifetime

1. Average cell: 7 to 10 years!

2. Short lived: Neutrophils: 2 days, red blood cells, 120 days

3. Long lived: neurons, eye lens cells — life time

NB: medium: muscles 16 years, skeletal cells 15 years, fat cells, 8 years.

How Many Cells Are in Your Body? Probably More Than You Think! — Eppendorf Handling Solutions

Sperm Cells — Definition, Function, Structure, Adaptations, Microscopy

Egg meets sperm (article) | Embryology | Khan Academy

What cells in the human body live the longest?

» How big is a human cell?

Click here for the last three years of posts arranged by theme:

PDF with headlines — Google Drive


So what are your personal favorite magic numbers? What do they stand for? Please share the coolest thing you learned this week related to math, statistics, or numbers in general. Or, even better, the coolest or most important thing you learned in your life related to math.

This is your chance to make someone else’s day. And to consolidate in your memory something you might otherwise forget. Or to think more deeply than otherwise about something dear to your heart. Continuity is key to depth of thought.


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