pH from pOH Calculator

pH + pOH = 14 at 25°C. Convert one to the other.

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How to use this calculator

  • Pick conversion direction.
  • Enter the value.
  • Read the converted result.

About this calculator

In water at 25°C, pH + pOH = 14. This is the auto-ionization product Kw = [H⁺][OH⁻] = 10⁻¹⁴. Take the negative log of both sides and you get the additive form. Use this to switch between pH and pOH whenever convenient.

Frequently asked

Does pH + pOH = 14 always?+
At 25°C in water, yes. At other temperatures the constant changes slightly — at 0°C it's ~14.94; at 100°C it's ~12.46.
Why pOH at all?+
For basic solutions, pOH is a more natural number. NaOH 0.01 M gives pOH = 2 (cleaner) vs pH = 12.
How do strong base pH calcs work?+
Compute pOH = -log[OH⁻] from base concentration, then pH = 14 - pOH.
Does this depend on solvent?+
Yes — only water gives Kw = 10⁻¹⁴. Other solvents have different self-ionization constants.
Can pOH be negative?+
Yes — strong base [OH⁻] > 1 M gives negative pOH (and pH > 14).

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