Ksp Molar Solubility Calculator
The solubility product constant, Ksp, describes the equilibrium between an undissolved ionic solid and its dissolved ions. Given the salt stoichiometry (the number of cations and anions per formula unit) and a measured Ksp value, you can compute the molar solubility, the moles of solid that dissolve per liter to saturate pure water. This calculator solves the general expression Ksp = m^m * n^n * s^(m+n) for s, covering 1:1 salts like AgCl, 1:2 salts like CaF2, and any other ratio you enter. Provide your own Ksp because that value is empirical and temperature dependent.
Ksp to molar solubility formula
Dissolution: MmXn(s) gives m M(+) + n X(-)
At saturation: [M] = m*s and [X] = n*s
Ksp = (m*s)^m * (n*s)^n
Ksp = m^m * n^n * s^(m+n)
s = (Ksp / (m^m * n^n))^(1 / (m + n))
Once s is known, the saturated ion concentrations follow directly: the cation concentration is m times s and the anion concentration is n times s.
Notes on solubility products
- Ksp values are conventionally tabulated at 25 degrees Celsius and change with temperature.
- A 1:1 salt (m = n = 1) reduces to s = sqrt(Ksp).
- A 1:2 salt such as CaF2 (m = 1, n = 2) gives s = (Ksp / 4)^(1/3).
- The model assumes pure water, no common ions, and ideal (unit activity) behaviour.
- Ion pairing and complex formation can make measured solubility higher than this idealised value.
Ksp solubility: frequently asked questions
What is Ksp?
Ksp is the solubility product constant, the equilibrium constant for the dissolution of a sparingly soluble ionic solid into its constituent ions in water. For a salt that dissolves into cations and anions, Ksp equals the product of the ion concentrations each raised to the power of its stoichiometric coefficient at saturation.
How do you find molar solubility from Ksp?
For a salt that dissolves to give m cations and n anions, the saturated concentrations are m*s and n*s where s is the molar solubility. Substituting into Ksp = (m*s)^m * (n*s)^n gives Ksp = m^m * n^n * s^(m+n). Solving for s gives s = (Ksp / (m^m * n^n))^(1/(m+n)).
What units does molar solubility use?
Molar solubility s is expressed in moles per liter (mol/L). It represents how many moles of the solid dissolve per liter of solution before the solution becomes saturated, assuming no common-ion effect and ideal behaviour.
Does this account for the common-ion effect?
No. This calculator assumes the salt dissolves in pure water with no pre-existing common ions and assumes activity coefficients of 1. The common-ion effect, ion pairing, and complexation can substantially reduce real solubility. Use measured values for precise work.
Where do Ksp values come from?
Ksp values are empirical and temperature dependent, typically tabulated at 25 degrees Celsius. Because they are measured constants that vary by source and conditions, you enter the Ksp value yourself rather than the calculator hardcoding any figure.
Official sources
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.