pH Calculator
Calculate pH from hydrogen ion concentration, or the concentration from pH, plus pOH and hydroxide concentration for acids and bases.
Last reviewed by the Radiatus Cloud team
Calculate pH, pOH and ion concentrations for a solution.
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Calculate pH and pOH
The pH scale measures how acidic or basic a solution is, based on the concentration of hydrogen ions. pH is defined as the negative base-ten logarithm of the hydrogen ion concentration in moles per litre. This calculator converts between hydrogen ion concentration and pH in both directions, and also gives the pOH and the hydroxide ion concentration, since pH and pOH always sum to fourteen in water at standard conditions. A hydrogen ion concentration of ten to the minus four gives a pH of four, which is acidic.
Because the scale is logarithmic, each whole-number change in pH represents a tenfold change in acidity.
The pH scale
pH is fundamental across chemistry, biology, medicine, agriculture and environmental science. A pH below seven is acidic, above seven is basic or alkaline, and exactly seven is neutral, like pure water. The logarithmic nature of the scale means a solution of pH three is ten times more acidic than pH four and a hundred times more acidic than pH five, which is easy to underestimate.
This calculator assumes standard conditions where pH and pOH sum to fourteen. For strong acids and bases the hydrogen or hydroxide concentration can be taken directly from the molarity. All calculation happens locally in your browser.
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Frequently Asked Questions
What is the pH formula?
pH equals the negative base-ten logarithm of the hydrogen ion concentration in moles per litre.
What do pH values mean?
Below seven is acidic, above seven is basic or alkaline, and exactly seven is neutral. Pure water is neutral at pH seven.
How are pH and pOH related?
In water at standard conditions they always add up to fourteen, so knowing one gives the other immediately.
Why is the pH scale logarithmic?
Because it is based on a logarithm, each unit represents a tenfold change in hydrogen ion concentration and hence in acidity.
Can I go from pH back to concentration?
Yes. The hydrogen ion concentration equals ten raised to the negative pH, which the tool calculates when you enter a pH.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Enter a hydrogen ion concentration or a pH value.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.