Ionic concentrations expressed in parts per million (ppm) or milligrams per liter (mg/l) must be converted to milli-equivalents per liter prior to constructing a Piper, Stiff, or Durov diagram, or computing ion balances.
The conversion factor is 1/equivalent weight of the ion. The ion's equivalent weight is its formula weight in grams divided by its electrical charge or valence.
Here are some conversion factors for common ions. Those listed in bold type are the standard ions used by the RockWorks program; those in regular type are possible additional ions that you can declare using the Additional Ions setting in the Piper Diagram, Stiff Diagram, Durov Diagram, Stiff Map, and Ion Balance windows.
Cations:
Anions
! Note that SiO2 is a common dissolved solid in water solutions, but is not ionic. It may be listed as an "additional ion" in either the Cation or Anion side, with a conversion factor of "0".