In organic chemistry and biochemistry it is customary to use pK values for acid dissociation equilibria.
where log denotes a logarithm to base 10 or common logarithm, and K is a stepwise acid dissociation constant. For bases, the base association constant, pK is used. For any given acid or base the two constants are related by , so pK can always be used in calculations.
On the other hand, stability constants for metal complexes, and binding constants for host–guest complexes are generally expressed as association constants. When considering equilibria such as
:M + HL  ML + H
it is customary to use association constants for both ML and HL. Also, in generalized computer programs dealing with equilibrium constants it is general practice to use cumulative constants rather than stepwise constants and to omit ionic charges from equilibrium expressions. For example, if NTA, nitrilotriacetic acid, N(CHCOH) is designated as HL and forms complexes ML and MHL with a metal ion M, the following expressions would apply for the dissociation constants.
The cumulative association constants can be expressed as
Note how the subscripts define the stoichiometry of the equilibrium product.