Here's a quick breakdown:

* Bacteria: These are single-celled organisms that can be seen with a light microscope. They range in size from about 0.5 to 10 micrometers (µm).

* Viruses: These are much smaller, non-living entities that require a host cell to replicate. They are typically measured in nanometers (nm) and range from 20 to 400 nm in size.

Think of it this way:

* A bacteria is like a tiny, single-room house.

* A virus is like a small, single-person car.

Let me know if you'd like to know more about bacteria or viruses!