pH Calculator
Calculate pH, pOH, and ion concentrations easily. Select the calculation type below.
Calculate pH from Hydrogen Ion Concentration
Calculate pOH from Hydroxide Ion Concentration
Calculate Ion Concentration from pH
Understanding pH
The pH scale is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. It ranges typically from 0 to 14, where 7 is neutral. Values less than 7 indicate acidity, while values greater than 7 indicate alkalinity (basicity).
The pH Formula
The pH is calculated as the negative base-10 logarithm of the activity of hydrogen ions in a solution:
pH = -log[H+]
Where [H+] represents the concentration of hydrogen ions in moles per liter (mol/L).
pOH and the Ion Product of Water
Just as pH measures hydrogen ions, pOH measures the concentration of hydroxide ions ([OH-]). In aqueous solutions at 25°C, the sum of pH and pOH is always equal to 14:
pH + pOH = 14
This relationship allows you to calculate one if you know the other. The ion product of water (Kw) is 1.0 × 10⁻¹⁴ at 25°C.