pH Calculator
Hand it a hydrogen ion concentration and it returns pH and pOH — or flip the switch and go from a pH value back to [H+] and [OH-].
pH
3
pOH
11
[H⁺]
0.001mol/L
[OH⁻]
0mol/L
How it works
pH is a compact way to write concentration on a log scale: pH = -log10([H+]). Each whole step down means ten times more hydrogen ions, which is why pH 2 is a hundred times more acidic than pH 4.
Going the other direction just undoes the log: [H+] = 10^-pH. The tool runs it both ways depending on which mode you pick, and it refuses to take the log of zero or a negative concentration — those get a dash instead.
pOH rides along automatically. In water at room temperature pH + pOH = 14, so pOH = 14 - pH, and [OH-] comes from 10^-pOH. Together they tell you how acidic or basic the solution is.
Frequently asked questions
What does a pH of 7 mean?
A pH of 7 is neutral at room temperature — hydrogen and hydroxide ions are balanced. Below 7 is acidic, above 7 is basic, and each unit is a tenfold change in [H+].
How do I find the pH of a strong acid?
A strong acid fully dissociates, so [H+] is essentially its molarity. Enter that concentration and read off the pH — a 0.001 M strong acid lands right around pH 3.
How is pOH related to pH?
In water at 25 °C they always sum to 14, so pOH = 14 - pH. For a strong base it's often easier to start from [OH-], get pOH, then subtract from 14 to reach the pH.