🧫pH & pOH Calculator
Convert between pH, pOH, [H⁺], and [OH⁻] using pH + pOH = 14 and [H⁺][OH⁻] = Kw.
Free pH & pOH Calculator
Our free pH calculator chemistry tool converts instantly between pH, pOH, [H⁺], and [OH⁻]. Enter any one of the four values and it calculates the other three using the standard 25°C relationships pH + pOH = 14 and [H⁺][OH⁻] = Kw, with an option to adjust Kw for non-standard temperatures.
Switch to strong acid/base mode to enter a molar concentration directly and get its pH immediately, assuming full dissociation. Results display in proper scientific notation, and a visual acid-base scale shows exactly where your solution falls between strongly acidic and strongly basic.
Ideal for chemistry homework, lab prep, or a quick sanity check — runs entirely in your browser. No sign-up, no downloads, no limits.
About the pH & pOH Calculator
Features
Four-way conversion
Enter any one of pH, pOH, [H⁺], [OH⁻] to get the other three.
Strong acid/base mode
Enter a molar concentration directly to get pH, assuming full dissociation.
Temperature-adjustable Kw
Adjust Kw for conditions other than the standard 25°C.
Visual acid-base scale
See at a glance where your solution falls between acidic and basic.
Frequently Asked Questions
How does the pH & pOH calculator work?
Enter pH, pOH, [H+], or [OH-]; it calculates the other three using pH + pOH = 14 and [H+][OH-] = Kw.
Is it free?
Completely free, no sign-up, downloads, or limits.
Can I calculate pH from a strong acid's concentration?
Yes, using the strong acid/base concentration mode, which assumes full dissociation.
Does it work at temperatures other than 25°C?
Yes, you can adjust Kw for other temperatures instead of assuming the standard 10⁻¹⁴ value.
Does it handle scientific notation?
Yes, [H+] and [OH-] inputs and outputs support scientific notation.
What does the visual scale show?
Where your solution falls on the 0-14 acid-base spectrum, labelled acidic, neutral, or basic.
Does it work for weak acids or bases?
Not directly — weak acid/base pH depends on Ka/Kb equilibrium, which this tool doesn't model; it's for pH/pOH/ion conversions and strong acid/base concentrations.
What if I enter a negative concentration?
It's flagged as invalid, since concentrations can't be negative.
Is my data stored?
No; everything runs in your browser and isn't stored or sent anywhere.
Does it work on mobile?
Yes, fully responsive on all screen sizes.