pH Calculator

What pH, pOH, and ion concentration describe

pH is the negative base-10 logarithm of the hydrogen ion concentration in moles per liter. A one-unit drop in pH means the solution is ten times more acidic. At 25 °C, pH and pOH add to 14 because the water equilibrium constant Kw is \(1.0 \times 10^{-14}\).

$$[\mathrm{H}^+] = 10^{-\mathrm{pH}}$$

$$[\mathrm{OH}^-] = 10^{-\mathrm{pOH}} \quad \text{and} \quad \mathrm{pH} + \mathrm{pOH} = 14$$

How to read the result

Enter a pH, a pOH, or a hydrogen ion concentration. The calculator updates the other three values, labels the solution acidic, neutral, or basic, and marks the nearest whole number on a 0 to 14 color scale. Values outside 0 to 14 still convert, and the scale note says they sit beyond the usual aqueous range.

The reference list loads approximate textbook pH values for common liquids so you can compare a reading. Those anchors are not a substitute for a calibrated meter. For buffer recipes, use the Buffer pH Calculator. To go from Ka to pKa, use the pKa Calculator, and for preparing solutions by moles per liter use the Molarity Calculator.

Worked example

A pH of 4.20 corresponds to \([\mathrm{H}^+] = 6.310 \times 10^{-5}\) mol/L. pOH is 9.80, and \([\mathrm{OH}^-] = 1.585 \times 10^{-10}\) mol/L. The solution is acidic.