pOH Calculator

pOH, pH and both ion concentrations, with the 14 explained.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

I know the

Value

pOH

pH 3 · acidic

pOH11

pH3

[H⁺]0.001 M

[OH⁻]1.0000e-11 M

pH + pOH14

pOH is the hydroxide mirror of pH, and at 25 °C the two sum to 14 because that is the negative logarithm of water's ion product. That 14 is not a constant of nature: Kw rises with temperature, so at 50 °C the sum is nearer 13.3 and neutral water sits at pH 6.6 while remaining exactly neutral. Neutrality means equal ion concentrations, not pH 7.

How the pOH Calculator works

pOH is the hydroxide mirror of pH, and at 25 °C the two sum to 14 because that is the negative logarithm of water's ion product. That 14 is not a constant of nature — it shifts with temperature.

Also known as: ph to poh converter · hydroxide ion concentration calculator · poh formula · how to calculate poh

Where to go next

The pOH question rarely arrives on its own. These are the ones that usually come with it:

pH Calculator — pH, pOH and both ion concentrations, on a log scale.
Henderson-Hasselbalch Calculator — Buffer pH, and where the buffer stops buffering.
Weak Acid pH Calculator — Solved exactly, without the x ≪ C approximation.
Speed Distance Time Calculator — Any one of the three from the other two, in four units.

Sources

Frequently asked questions

How do I convert pH to pOH?

Subtract from 14 at 25 °C. A pH of 3 is a pOH of 11.

Why do pH and pOH sum to 14?

Because water's ion product Kw is 10⁻¹⁴ at 25 °C. Taking negative logarithms of both sides gives pH + pOH = 14.

Does that sum change?

Yes. Kw rises with temperature, so at 50 °C the sum is nearer 13.3 and neutral water sits at pH 6.6 while remaining exactly neutral. Neutrality means equal ion concentrations, not pH 7.

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