pH to Hydrogen Ion Concentration Calculator
Convert a pH value into the hydrogen ion concentration [H⁺] in mol/L, with matching pOH and [OH⁻].
How it works
[H⁺] = 10^(−pH) · pOH = 14 − pH · [OH⁻] = 10^(−pOH)
pH is defined as the negative base-10 logarithm of the hydrogen ion activity, so reversing it is a simple power of ten. Because each pH unit is a factor of ten, a pH of 3 has ten times more H⁺ than a pH of 4. At 25 °C the ion product of water fixes pH + pOH = 14, which lets you find [OH⁻] from the same value.
Worked example
For pH 3: [H⁺] = 10⁻³ = 0.001 mol/L. Then pOH = 14 − 3 = 11 and [OH⁻] = 10⁻¹¹ = 1.0 × 10⁻¹¹ mol/L.
Sources: pH — Wikipedia
Frequently asked questions
Why is [H⁺] so small at high pH?
The scale is logarithmic, so each rise of one pH unit divides the hydrogen ion concentration by ten. By pH 11 the [H⁺] has fallen to 10⁻¹¹ mol/L — a hundred-million-fold below pH 3.
Does the pH + pOH = 14 rule always hold?
Only at 25 °C. The ion product of water (Kw) changes with temperature, so the sum shifts — for example it is about 13.6 at 50 °C.
Can pH be negative?
Yes. Very concentrated strong acids can have [H⁺] above 1 mol/L, which gives a negative pH. The formula still applies.
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