MasterTool

pH Calculator

Calculate the pH of a strong acid or strong base from its molarity — with pOH and both ion concentrations.

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What this tool does

Calculate the pH of a strong acid or strong base from its molarity — with pOH and both ion concentrations. Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.

How to use the pH Calculator

  1. Enter or select solution.
  2. Enter or select concentration (mol/l).
  3. Enter or select ionisable h⁺ / oh⁻ per formula unit (1 for hcl/naoh, 2 for h₂so₄).
  4. Read the calculated result; change any measurement to compare alternatives.

Formula

pH = −log₁₀[H⁺]; for a strong base pOH = −log₁₀[OH⁻] and pH + pOH = 14 at 25 °C. Strong acids and bases are treated as fully dissociated, so [H⁺] = concentration × protons per formula unit.
kind
Solution
conc
Concentration (mol/L)
protons
Ionisable H⁺ / OH⁻ per formula unit (1 for HCl/NaOH, 2 for H₂SO₄)

Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.

Worked example

For ph calculator, the following measurements illustrate the exact method: Solution: acid; Concentration (mol/L): 0.01; Ionisable H⁺ / OH⁻ per formula unit (1 for HCl/NaOH, 2 for H₂SO₄): 1.

Inputs

  • SolutionStrong acid (e.g. HCl)
  • Concentration (mol/L)0.01
  • Ionisable H⁺ / OH⁻ per formula unit (1 for HCl/NaOH, 2 for H₂SO₄)1

Result

  • pH2
  • pOH12
  • [H⁺] (mol/L)0.01
  • [OH⁻] (mol/L)0
  • CharacterAcidic

Results explained

pH
pH from the formula above. Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.
pOH
pOH from the formula above. Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.
[H⁺] (mol/L)
[H⁺] (mol/L) from the formula above. Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.
[OH⁻] (mol/L)
[OH⁻] (mol/L) from the formula above. Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.
Character
Character from the formula above. Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.

Frequently asked questions

pH = −log₁₀[H⁺]; for a strong base pOH = −log₁₀[OH⁻] and pH + pOH = 14 at 25 °C. Strong acids and bases are treated as fully dissociated, so [H⁺] = concentration × protons per formula unit.

Strong electrolytes only, at 25 °C where Kw = 10⁻¹⁴ and neutral pH is exactly 7. Very dilute solutions (below ~10⁻⁶ M) are pulled toward 7 by water's own autoionisation, and concentrated solutions need activity corrections — both are beyond this model.

Sulfuric acid's first proton dissociates completely but the second only partially (Ka₂ ≈ 0.012), so [H⁺] lands a little below 0.04 M. This calculator has a protons-per-formula field as a first approximation; exact diprotic calculations need the Ka₂ equilibrium.

Yes — the 0–14 range is just where dilute everyday solutions fall. A 10 M strong acid has pH ≈ −1 and 10 M NaOH has pH ≈ 15.

Every field is labelled with its unit — enter values in exactly the labelled unit and read the result in the labelled output unit. Fields with a unit symbol also support the site-wide imperial/metric switch, which converts before the formula runs.

It uses double-precision arithmetic and the published constants and formulas named on this page. The last displayed digit may be rounded, and real conditions can differ from the idealized model described in the assumptions.

Yes. Every calculation runs entirely in your browser; nothing you enter is uploaded, stored or shared.