pH Calculator

Convert between [H⁺], [OH⁻], pH, and pOH — enter any one and see the rest. Calculates in your browser.

pH

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pOH-
[H⁺]-
[OH⁻]-

Show the math

pH measures hydrogen-ion concentration on a log scale:

pH = −log₁₀[H⁺]  ·  pH + pOH = 14

Below 7 is acidic, 7 is neutral, above 7 is basic (at 25 °C). All math runs in your browser.

What this does

A pH calculator converts between [H⁺], [OH⁻], pH, and pOH — enter any one and see the rest.

How to use it

  1. Enter a concentration or a pH/pOH.
  2. Read the other three values.
  3. Compare against the 0–14 scale.
  4. Check acidic, neutral, or basic.

How it works

pH is the negative base-10 logarithm of hydrogen-ion concentration. Below 7 is acidic, 7 is neutral, above 7 is basic.

pH = −log₁₀[H⁺]; pH + pOH = 14 (at 25°C)

Understanding your result

Because pH is a logarithm, each whole unit is a tenfold change in hydrogen-ion concentration, so a pH of 4 is ten times more acidic than 5, not a little. Below 7 is acidic, 7 neutral, above 7 basic, and the pH-plus-pOH-equals-14 rule holds at 25 degrees C; at other temperatures neutral is not exactly 7, which trips up precise work.

Example

A 1×10⁻³ M [H⁺] solution has a pH of 3.

Sources & methodology

Last updated .

Frequently asked questions

How is pH defined?

pH is the negative base-10 logarithm of hydrogen-ion concentration: pH = −log₁₀[H⁺].

How are pH and pOH related?

At 25 °C they sum to 14: pH + pOH = 14. Below 7 is acidic, 7 is neutral, above 7 is basic.

Is my data stored?

No. Everything is calculated locally in your browser.