The Ring Double Bond Equivalents (RDBE) value, which estimates the number of rings and
unsaturated bonds in a molecule, can be calculated from a chemical formula using
the following general equation:
where ni is the number of atoms and νi the formal valence of the element i.
Theoretically, each ring or a double bond increases the RDBE value by 1,
while each triple bond increases the value by 2.
This equation can only be used for formulas composed of elements with a well-defined formal valence.
A number of exceptions to the RDBE rule are known, however the RDBE value still provides a useful indicator regarding the validity of a molecular formula.