Size measures for items related to cells

This page lists order of magnitude estimates for the sizes of various microscopic items that are related to cells. The goal is to give a rough sense of what individual sizes mean, since these are too small for us to compare with our day-to-day intuitions.

Units for length

Units

Unit for length (full word)	Unit for length (shorthand)	In terms of meters (m)	What's it used to measure?
femtometer	fm	$10^{-15}$	nucleus of an atom (not nucleus of a cell). Rarely used in biology
picometer	pm	$10^{-12}$	radius and diameter of an atom or size of a molecule. Used in biology when talking about biological membranes and passage of ions through membranes
angstrom	A	$10^{-10}$	sizes of molecules, wavelengths of light
nanometer	nm	$10^{-9}$	sizes of very large molecules, substructures and organelles of cells, wavelengths of light
micron or micrometer	$\mu$m	$10^{-6}$	sizes of cells and cellular organelles
millimeter	mm	$10^{-3}$	Rarely used in cell biology. May be used for tissues and cell clusters

Conversion between units

Unit for length (full word)	Unit for length (shorthand)	Number of fm	Number of pm	Number of angstroms	Number of nm	Number of $\mu$m	Number of mm
femtometer	fm	1	$10^{-3}$	$10^{-5}$	$10^{-6}$	$10^{-9}$	$10^{-12}$
picometer	pm	$10^3$	1	$10^{-2}$	$10^{-3}$	$10^{-6}$	$10^{-9}$
angstrom	A	$10^5$	$10^2$	1	$10^{-1}$	$10^{-4}$	$10^{-7}$
nanometer	nm	$10^6$	$10^3$	10	1	$10^{-3}$	$10^{-6}$
micron or micrometer	$\mu$m	$10^9$	$10^6$	$10^4$	$10^3$	1	$10^{-3}$
millimeter	mm	$10^{-3}$	$10^{12}$	$10^9$	$10^7$	$10^6$	$10^3$	1