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Ksp to Solubility Calculator

Enter the solubility product Ksp to get the molar solubility of a 1:1 salt.

How it is calculated

For a salt that dissolves as one cation and one anion, AB ⇌ A⁺ + B⁻, the solubility product is Ksp = [A⁺][B⁻]. If s mol/L dissolves, both ion concentrations equal s, so Ksp = s² and s = √Ksp. The tool takes the square root of the Ksp you enter and prints the molar solubility in mol/L.

Ksp must be greater than zero (zero and negative values show no result), and you can type it in scientific notation such as 1.8e-10. Results of 0.001 mol/L or more are printed with six decimals; smaller ones switch to scientific notation with four significant figures, such as 1.342 × 10⁻⁵ mol/L. The formula is valid only for a 1:1 salt (AgCl, BaSO₄); a salt like CaF₂ or Ag₂CrO₄ has a different relationship and would need a cube root with a factor. It also assumes pure water and ignores common ions and complex formation.

Worked example

A 1:1 salt has Ksp = 1.8 × 10⁻¹⁰, entered as 1.8e-10. Then s = √(1.8 × 10⁻¹⁰) = 1.342 × 10⁻⁵. The tool shows 1.342 × 10⁻⁵ mol/L. Check by squaring: (1.342 × 10⁻⁵)² ≈ 1.8 × 10⁻¹⁰. If you want grams per litre, multiply by the molar mass; for a salt of 100 g/mol that is about 0.0013 g/L (1.342 × 10⁻⁵ × 100).

Try this example →

Common mistakes

  • Using the tool for salts that do not split 1:1, like CaF₂ (1 Ca²⁺ + 2 F⁻) or Ag₃PO₄. For those, Ksp is not s².
  • Entering the Ksp as a positive exponent or dropping the minus sign, such as 1.8e10 instead of 1.8e-10. The Ksp of a sparingly soluble salt is far below 1, and 1.8e10 would give a huge, meaningless solubility.
  • Reading the result as grams per litre. The unit is mol/L, so multiply by the molar mass for g/L.
  • Applying the answer to a solution that already contains one of the ions. A common ion lowers solubility, and this tool assumes pure water.
  • Reading 1.342 × 10⁻⁵ as 1.342 × 10⁵ or as 1.342 × 10⁻⁶. The superscript exponent matters far more than the digits before the multiplication sign.

About this calculator

This calculator finds the molar solubility of a sparingly soluble 1:1 ionic salt (like AgCl or CaSO₄) from its solubility product constant, Ksp, using s = √Ksp. This comes directly from the equilibrium expression: for a salt that dissociates as AB ⇌ A⁺ + B⁻, Ksp = [A⁺][B⁻] = s × s = s².

Ksp is an equilibrium constant that describes how far a sparingly soluble salt dissolves in water before the solution becomes saturated, and converting it to molar solubility (mol/L) — and from there to g/L — tells a chemist exactly how much of the solid will actually dissolve. It's a foundation-level calculation in analytical and general chemistry, used for predicting precipitation reactions and interpreting solubility rules.

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Comments (1)

  • Editorial team

    This takes the square root of Ksp, which is right only for salts that split into one cation and one anion, such as BaSO4. A Ksp of 1.1e-10 gives 1.049 × 10⁻⁵ mol/L. A salt such as CaF2 releases three ions, so the square-root answer would be wrong for it. The common-ion effect and activity also change real solubility. Which salt types, such as 1:2, should we support?

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