Solubility Product (Ksp) Calculator
The solubility product Ksp measures how far a sparingly soluble salt dissolves at equilibrium. For a salt that splits into a cations and b anions per formula unit, the ion concentrations are a and b times the molar solubility, and Ksp is their product raised to the matching powers. This calculator takes the molar solubility and the two stoichiometric coefficients and returns Ksp, the cation and anion concentrations, and the ionic strength contribution. Enter whole-number coefficients to match your balanced dissolution equation.
Solubility product formula
cation conc = a * s
anion conc = b * s
Ksp = (a * s)^a * (b * s)^b
pKsp = -log10(Ksp)
Here s is molar solubility, a is the number of cations and b the number of anions released per formula unit. For a 1:1 salt this reduces to Ksp = s squared; for a 1:2 salt to Ksp = 4 s cubed.
Worked example: silver chloride
- AgCl dissolves into one Ag+ and one Cl- (a = 1, b = 1).
- Molar solubility is about 1.34e-5 mol/L.
- Both ion concentrations equal s = 1.34e-5 mol/L.
- Ksp = s squared = (1.34e-5)^2 = 1.80e-10.
- pKsp = -log10(1.80e-10) = 9.74.
Solubility product: frequently asked questions
What is the solubility product Ksp?
The solubility product Ksp is the equilibrium constant for a sparingly soluble ionic solid dissolving in water. For a salt that dissolves into ions, Ksp is the product of the equilibrium ion concentrations, each raised to its stoichiometric coefficient. A smaller Ksp means a less soluble salt.
How is Ksp found from molar solubility?
For a salt A(a)B(b) that gives a cations and b anions per formula unit, the cation concentration is a times the molar solubility s and the anion concentration is b times s. Then Ksp = (a s) raised to a, times (b s) raised to b. This calculator applies that for any whole-number a and b.
What is molar solubility?
Molar solubility s is the number of moles of the solid that dissolve per litre of solution to reach saturation. It is the amount of formula units dissolved, before splitting into ions. Multiplying by the ion coefficients gives the actual ion concentrations.
Why does a 1:1 salt give Ksp equal to s squared?
For a salt like AgCl that releases one cation and one anion (a = 1, b = 1), both ion concentrations equal s, so Ksp = s times s = s squared. For a 1:2 salt the anion concentration is 2s, giving Ksp = s times (2s) squared = 4 s cubed.
Official sources
- NIST Chemistry WebBook: solubility and equilibrium reference data.
- IUPAC Gold Book: solubility product constant definition.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.