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pH Calculator
Find pH, pOH and ion concentrations for strong acids, strong bases and weak acids.
pH of a solution
pH: —
pOH: —
Hydrogen ion concentration: —
Hydroxide ion concentration: —
How to use the pH Calculator
- Choose whether you have an acid, a base, a pH value or a Ka.
- Enter the concentration, the pH or the dissociation constant.
- Read the pH, pOH and ion concentrations from the result panel.
Features
- Strong acids, strong bases and weak acids
- Reports pH, pOH, hydrogen and hydroxide ions
- Uses pH + pOH = 14 at 25 degrees
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online ph calculator.
Take the negative base ten logarithm of the hydrogen ion concentration. For 0.01 mol/L that
logarithm is minus two, so the pH is 2.
Hydrochloric acid is a strong acid that dissociates fully, so the hydrogen ion concentration
is 0.01 mol/L and the pH is exactly 2.
At 25 degrees Celsius pH plus pOH always equals 14, so a pH of 3 means a pOH of 11 and the
other way round.
Raise ten to the power of the negative pH. A pH of 4 gives a hydrogen ion concentration of
0.0001 mol/L.
Weak acids only partly dissociate, so the tool uses the acid dissociation constant Ka with
the square root approximation to find pH.
A pH below 7 is acidic, a pH of 7 at 25 degrees Celsius is neutral, and a pH above 7 is basic
or alkaline.
No. All of the pH arithmetic happens locally in your browser and no values are ever sent
anywhere.
Yes. The neutral point shifts with temperature, so the rule that pH plus pOH equals 14 holds
closely only near 25 degrees Celsius.
Last updated: October 10, 2026