# mass of bacteria

Graham Shepherd muhero.nospam at globalnet.co.uk
Wed Apr 3 20:16:06 EST 2002

```Smarty <smartman at comcast.net> wrote in message
news:3cab7bd6.18969629 at news.in.comcast.giganews.com...
> Less than 500 milligrams
>

You can get an approximation by calculating the volume of the organism from
typical dimensions (eg for E.coli assume it's a cylinder 1 micron long with
a diameter of 0.5 micron) and assume that the density is the same as water.
(It is greater, otherwise you couldn't spin them down - but it's probably
not much greater. You could determine the density on a gradient if it's
critical).

A rough calculation indicates that the volume is about 0.2 cubic microns.
That's 5,000,000,000 per cubic millimeter, or 5,000,000,000,000 per cubic
cm. Assuming 1 gram per cubic cm, one bacterium weighs about 0.2 picogram.

Viruses are much more variable in size than bacteria (the biggest viruses
are bigger than the smallest bacteria). But you could do the same
calculation for a specific virus.

GS

```