Microorganisms on and in your body are incredibly tiny—most are so small that millions could fit on the head of a pin.

How Small Are These Microorganisms?

Typical size range

Most of the microbes that live on and in the human body (especially bacteria) fall in this rough size range:

  • Bacteria: about 0.5 to 5 micrometers in length (1 micrometer is one‑millionth of a meter).
  • Common human cells: about 10–20 micrometers across, so a human cell is often several times larger than a bacterial cell.
  • Viruses (also part of the human microbiome): roughly 20–300 nanometers, which is about 10–100 times smaller than many bacteria.

A helpful way to picture it: if a typical human cell were the size of a cantaloupe , many bacteria would be more like blueberries around it.

Where Are These Microbes Living?

Your personal “microbe cloud” is called the human microbiome , and it lives:

  • On the skin (including the face, scalp, armpits, and feet).
  • In the mouth (saliva, tongue, dental plaque).
  • Throughout the gut , especially the large intestine, which contains the densest populations.
  • In other moist areas like the nose and urogenital tract.

Even though these organisms are tiny, there are roughly 39 trillion microbial cells living with you, a number similar to your total human cell count.

How Tiny Are They Compared to You?

To get a sense of scale:

  1. A human hair is about 70 micrometers thick, so many common bacteria are about 1/100 the width of a hair.
  1. Because they’re so small, all the bacteria in your body together weigh only about 1–3% of your body mass, even though they number in the tens of trillions.
  1. You could fit dozens of bacteria across the diameter of a single human cell.

Mini Story: A Walk on Your Skin

Imagine shrinking down until your height is one micrometer.
You step out onto a patch of your forearm:

  • The “ground” is a landscape of skin cells that, to you, look like boulders.
  • Between them are warm, moist crevices—perfect valleys where bacterial communities cluster and form biofilms.
  • Every droplet of sweat is like a pond, and a single flake of skin is a massive plateau teeming with life.

From that perspective, your body is less like a single organism and more like an entire planet for microscopic life, with different climates (oily, dry, acidic, oxygen‑poor) that select for different species.

Quick Facts at a Glance

  • Most body‑associated bacteria: 0.5–5 micrometers long.
  • Typical human cell: around 10 micrometers or more across.
  • Viruses in the microbiome: tens to hundreds of nanometers.
  • Total microbes on/in a person: about 39 trillion cells.
  • Their combined mass: roughly 1–3% of your body weight.

Information gathered from public forums or data available on the internet and portrayed here.