pH Calculator
Calculate pH, pOH, hydrogen ion concentration, hydroxide concentration, strong acid/base solution pH, dilution pH, buffer pH, and pKa values.
Quick answer: pH is -log10[H+]. At 25 C, pH + pOH = 14. For buffers, use pH = pKa + log10(base/acid).
Presets
Choose a mode and enter values.
pH Calculator Formulas
pH from concentration
pH = -log10[H+]
pOH relation
pH + pOH = 14 at 25 C
Hydrogen ion concentration
[H+] = 10^-pH
Buffer pH
pH = pKa + log10(base / acid)
When to Use Each pH Calculator Mode
- pH level calculator: use [H+] to pH or pH to [H+] modes.
- pOH and pH calculator: use pOH / [OH-] mode.
- Solution pH calculator: use strong acid/base mode for simple fully dissociated acids and bases.
- Buffer pH calculator: use Henderson-Hasselbalch mode for weak acid/conjugate base systems.
- pH to pKa calculator: use pKa from pH mode when base/acid ratio is known.
Assumptions: calculations use ideal behavior at 25 C unless stated otherwise. Pool pH adjustment, mixed acids/bases, ionic strength, activity coefficients, and real buffer capacity require more detailed chemistry than this educational calculator.