pOH to pH Calculator
Convert pOH to pH using the relationship pH + pOH = 14 (at 25 °C). Also shows H⁺ and OH⁻ concentrations. For education only.
How to use this tool
- Enter poh value in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your ph and the full breakdown beneath it.
At 25 °C, the ion-product constant of water gives: pH + pOH = 14. So if you know pOH, then pH = 14 − pOH. pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic.
For education only.
Formula
pH = 14 − pOH (at 25 °C)
[H+] = 10−pH mol/L
[OH−] = 10−pOH mol/L
How it works
This calculator uses the water autoionization equilibrium constant at 25 °C (Kw = 1 × 10−14), which gives the relationship pH + pOH = 14. Subtracting the entered pOH from 14 yields the pH; the ion concentrations are then derived from their respective negative-logarithm definitions.
The pH + pOH = 14 relationship strictly applies at 25 °C and standard pressure; at higher temperatures Kw increases, shifting the neutral point below 7. The solution is classified as acidic (pH < 7), neutral (pH = 7), or basic (pH > 7) based on the calculated pH.
Worked example
Worked example: converting pOH 4.0 to pH
- Identify input: pOH = 4.0.
- Apply the relationship: pH = 14 − 4.0 = 10.0.
- Classify: pH 10.0 > 7, so the solution is Basic (alkaline).
- Ion concentrations: [H⁺] = 10⁻¹⁰ mol/L; [OH⁻] = 10⁻⁴ mol/L.
pH = 10.0; Classification = Basic (alkaline)
Key terms
- pH
- The negative base-10 logarithm of the hydrogen ion concentration; ranges from 0 (very acidic) to 14 (very basic) at 25 °C.
- pOH
- The negative base-10 logarithm of the hydroxide ion concentration; pOH = −log[OH⁻].
- K_w (water ionization constant)
- The equilibrium constant for water's self-ionization: K_w = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25 °C, giving pH + pOH = 14.
- Acidic solution
- A solution with pH < 7 (at 25 °C), meaning [H⁺] > [OH⁻].
- Basic (alkaline) solution
- A solution with pH > 7 (at 25 °C), meaning [OH⁻] > [H⁺].
Frequently asked questions
- Why does pH + pOH = 14?
- Because Kw = [H⁺][OH⁻] = 1×10⁻¹⁴ at 25 °C. Taking −log of both sides: pH + pOH = 14.
- Does this hold at other temperatures?
- No — Kw changes with temperature. At 37 °C (body temp) pH + pOH ≈ 13.6.