The three main types of microbes are bacteria, viruses, and fungi. Out of these three, viruses are the smallest.

Here's a breakdown of their relative sizes:

* Bacteria: Typically range from 0.5 to 10 micrometers (µm) in size.

* Fungi: Can be much larger, with some species having hyphae (filaments) that extend for meters. However, individual fungal cells are usually in the same size range as bacteria.

* Viruses: Are much smaller than bacteria, ranging from 20 to 400 nanometers (nm) in size. (Remember, 1 µm = 1000 nm)

To put this in perspective, a typical virus is about 100 times smaller than a typical bacterium.