What is the solubility product constant (Ksp)?

Ksp is the equilibrium constant for the dissolution of a sparingly soluble ionic compound. For a salt MₓAᵧ dissolving into x M^(y+) cations and y A^(x-) anions, Ksp = [M]^x · [A]^y. Pure solids are not included in the expression.

How is molar solubility related to Ksp?

If s is the molar solubility (mol/L), then for an AB compound Ksp = s², for AB₂ Ksp = 4s³, for AB₃ Ksp = 27s⁴, etc. This calculator solves for s automatically given Ksp and compound type.

What is the reaction quotient (Q) and how does it relate to Ksp?

Q is computed the same way as Ksp but uses actual (non-equilibrium) concentrations. If Q Ksp, precipitation occurs; if Q = Ksp, the solution is at equilibrium.

Can I use this for compounds with custom stoichiometry?

Yes. Select "Custom" and enter positive integer exponents for the cation and anion. The calculator uses Ksp = [cation]^m · [anion]^n; fractional stoichiometric coefficients are not supported.

Does the common ion effect change Ksp?

Ksp itself is temperature-dependent and does not change with added ions. However, the presence of a common ion reduces molar solubility because the equilibrium shifts to favor the solid, which is why Q is useful for those scenarios.

Ksp Calculator

Calculate Ksp from ion concentrations or find molar solubility from a known Ksp for ionic compounds.

Calculation Mode

Compound Formula Type

Cation concentration (mol/L)

Anion concentration (mol/L)

Enter values and click Calculate to see results.

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Summary

The Ksp (solubility product constant) quantifies the equilibrium between a sparingly soluble ionic solid and its dissolved ions in aqueous solution. This calculator supports two modes: compute Ksp from measured ion concentrations, or determine molar solubility from a known Ksp value. It covers the most common compound formulas (AB, AB2, A2B, AB3, A2B3, A3B2) and lets you enter a custom stoichiometry.

How it works

Select the calculation mode: Ksp from concentrations, or molar solubility from Ksp.
Choose a preset compound formula or select "Custom" to enter your own cation/anion exponents.
Enter the required values (ion concentrations or Ksp) and click Calculate.
The result displays with the full equilibrium expression and a step-by-step breakdown.
Switch modes or change the compound type at any time to explore different scenarios.

Use cases

Predict whether a precipitate will form when two ionic solutions are mixed.
Determine molar solubility of a sparingly soluble salt for lab preparation.
Verify experimental ion concentration measurements against theoretical Ksp.
Solve general chemistry and analytical chemistry homework problems.
Compare solubility of different ionic compounds at a glance.
Support environmental chemistry calculations for water quality analysis.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu

Ksp Calculator

Result

Equilibrium Expression

Step-by-Step

Summary

How it works

Use cases

Frequently Asked Questions

Ksp Calculator

Use the Ksp Calculator

Result

Equilibrium Expression

Step-by-Step

Summary

How it works

Use cases

Frequently Asked Questions