pOH Calculator
Find pOH from hydroxide-ion concentration (or vice versa) and convert between pOH, pH, [OH-], and [H+] at 25 C.
Input quantity
mol/L
Basic (alkaline)
- 1
[OH⁻] concentration (mol/L)
1.000e-4Hydroxide ion concentration entered - 2
pOH = −log₁₀([OH⁻])
−log₁₀(1.000e-4) = 4 - 3
pH = 14 − pOH
14 − 4 = 10
How does this calculator work?
pOH measures hydroxide-ion concentration: pOH = -log10([OH-]). Enter [OH-] in mol/L to get pOH, or enter pOH to get [OH-]. At 25 C, pH + pOH = 14, so the tool also returns pH and [H+] = 10^(-pH). Lower pOH means a more basic solution.
Formula
How this is calculated
Choose whether you are entering the hydroxide-ion concentration [OH-] in mol/L or the pOH value directly. When [OH-] is supplied, pOH is the negative base-10 logarithm of that concentration, so a more concentrated base gives a lower pOH. When pOH is supplied, the concentration is recovered as [OH-] = 10^(-pOH).
The two scales are linked through the self-ionization of water. At 25 C the ion product Kw = [H+][OH-] = 1 x 10^-14, which means pH + pOH = 14. The calculator therefore reports pH = 14 - pOH and the hydronium concentration [H+] = 10^(-pH), giving you all four related quantities at once.
Results assume a temperature of 25 C and dilute aqueous solutions where activity equals concentration. Because Kw changes with temperature, the pH + pOH = 14 relationship holds only near 25 C. The [OH-] input must be positive (a logarithm of zero or a negative number is undefined), while pOH values normally fall between 0 and 14 for typical solutions.
Frequently asked questions
At 25 C, pH + pOH = 14 because the water ion product Kw equals 1 x 10^-14. Knowing one immediately gives the other.
The pH + pOH = 14 shortcut is specific to 25 C. Kw rises with temperature, so at other temperatures the sum differs and the conversions here become approximate.
A low pOH corresponds to a high hydroxide concentration, indicating a strongly basic (alkaline) solution. A pOH of 7 is neutral.
Also known as
TG we-Calculate Editorial Team. (2026). pOH Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/poh-calculator
TG we-Calculate Editorial Team. "pOH Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/poh-calculator.
TG we-Calculate Editorial Team, "pOH Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/poh-calculator
@misc{wecalculate_poh_calculator, title = {pOH Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/poh-calculator}}, year = {2026}, note = {TG we-Calculate} }
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