pH Calculator
pH from hydrogen ion concentration.
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Formula
pH = −log₁₀[H⁺]
pH is the negative base-10 logarithm of hydrogen ion activity. At 25°C, pOH = 14 − pH for aqueous solutions.
Worked example
[H⁺] = 10⁻³ mol/L gives pH = 3 — a moderately acidic solution.
Where this can give the wrong answer
- [H⁺] must be positive — pH of exactly 0 is possible for strong acids.
- Activity corrections matter in ionic strength solutions.
- Temperature shifts pKw — pOH relation assumes 25°C.
FAQ
- Yes for very concentrated strong acids where [H⁺] > 1 mol/L.