What is the size of 1 bacteria

Worksheet 1c: - How small / big are viruses?

Viruses: 15 to 400 nm (nanometers)
Bacteria: 0.3 to 1 µm (micrometers)
Human: 1.5 to 2 m (meters)

Small number prefixes:

10 -3                   10 -6                   10 -9                   10 -12                  10 -15

Milli- (m) micro- (µ) nano- (n) pico- (p) femto- (f)

400 nm = 0.4 µm
The largest viruses are as big as the smallest bacteria.

Most bacteria can be made visible with a light microscope. The resolution of the light microscope is not sufficient for viruses and very small bacteria. You need an electron microscope.

Resolving power of the human eye: 0.02 mm or 20 µm

I.e. if two lines are 0.02 mm apart, then we can just recognize them as two lines; when they are closer together we see them as a line.

Look at a ruler or graph paper. The smallest division is millimeters, one millimeter is 1000 µm or 50 by 20 µm. So imagine if a millimeter were again divided into 50 graduation lines. Our eyes are so good that they could still tell two lines apart.


  1. Measure the item handed out so that you can easily see it with the eye. Imagine a virus that size, can you imagine how big you would be in relation to that?
  2. Since it's hard to estimate, try to figure it out.

Example of a ratio calculation: someone is 2 meters tall, his pencil is 10 cm long. If the pencil were 1 meter long, the person would be proportionally 20 meters tall. Note the different units (nm, cm, mm, m)!

Use the back for your invoice and write down your result here: