It’s incredible to think that all you have to do is look up into the night sky, and you’ll see stars, planets, and galaxies that are thousands of light years away. Yet, we can’t see some objects that are right here on Earth.

As unpleasant as it is to think about, things like bacteria, germs, and dust mites are right under our noses. But they’re so small that they’re invisible to the naked eye.

This might leave you wondering about the smallest thing the human eye can see without the help of a microscope or magnifying glass. In this post, we’ll explore the answer.

Without using a magnifying glass or microscope, humans can see objects as small as 0.1 millimeters, which is about the same width as a strand of human hair.

When discussing the smallest thing the human eye can see, it’s important to explain that we’re defining a “thing” as an object in its own right. We’re not talking about things like smoke and fog, for example, as their tiny individual particles can only be seen with the human eye when they are grouped together.

Keep reading for more examples of tiny objects that can be seen without the help of equipment and the smallest things humans can see under a microscope.

Examples of tiny objects humans can see with the naked eye

As already mentioned, humans can see the width of a strand of hair without the aid of a magnifying glass or microscope. Here are some other examples of objects that are the same size as this:

How do these small objects compare to other small objects?

To put these small objects into perspective, here are some examples of what 0.1 millimeters is the equivalent of:

  • The thickness of a standard piece of paper
  • 12 times shorter than a medium-sized grain of sand
  • 17 times thinner than a strand of spaghetti
  • 140 times shorter than an aspirin
  • 13 times longer than a red blood cell
  • 17 times longer than an animal cell’s nucleus
  • 50 times longer than a rod-shaped E. coli bacterium

What tools are used to see tiny objects more clearly?

To see a strand of human hair, lice, human eggs, and amoeba in more detail, we need the help of equipment like magnifying glasses and microscopes. These tools are also used to see microscopic objects (objects that are smaller than 0.1 millimeters).

Magnifying glass

You can use a magnifying glass to see small objects more clearly, but you won’t be able to see the finer details. For this, you will need a more powerful tool, like a microscope.

Microscope

Light microscopes — also known as optical microscopes — have a series of lenses that enable you to see small cells easily and even make out some of the structures within the cells. To give you an idea of how small this is, more than ten red blood cells would fit on the tip of a human hair. However, cells are huge in relation to viruses, which light microscopes are not usually able to pick up.

What’s the smallest thing humans can see under a microscope?

With the help of a standard microscope, the human eye can see things that are as small as one micrometer. Also known as a micron, a micrometer is equal to 0.001 millimeters.

To see objects that are smaller than this, you would need an electron microscope. With an electron microscope, it is possible to see viruses, molecules, and even individual atoms! 

Cells measure from about 0.1 to 100 micrometers wide, while atoms are about 0.1 to 0.5 nanometers wide. A nanometer is 1,000 times smaller than a micrometer, which shows you just how small an atom is.

What does a micrometer look like?

There are 1,000 micrometers in a millimeter. A strand of human hair is 0.1 millimeters, which is equal to 100 micrometers. This means a micrometer is 100 times smaller than the width of a strand of hair. The eye of a fruit fly is 70 micrometers in diameter, and each eye is made up of 760 unit eyes measuring five micrometers across. As stated in the previous section, cells range from 0.1 to 100 micrometers wide. Human skin cells measure 20 to 40 micrometers across, white blood cells measure about 30 micrometers, and red blood cells average six to eight micrometers in width.

To find things that are one micrometer, though, we need to get sub-cellular. A human mitochondrion is one micrometer wide and seven micrometers long. Even smaller than that are bacteria, which can be as small as 0.5 micrometers.

Currently, humans may only be able to see objects as small as 0.1 millimeters without equipment, but with the help of microscopes, we can see much smaller objects. 

Many scientists are excited about the development of microscopy and believe there is no limit to how big an object has to be in order to be seen with the human eye. This concept would be especially important regarding research into the human body and treating diseases.