How is pH calculated?

pH is the negative base-10 logarithm of the hydrogen ion concentration in mol/L, so pH = -log10[H⁺]. A pH below 7 is acidic, 7 is neutral, and above 7 is basic at 25 °C.

How are pH and pOH related?

At 25 °C, pH + pOH = 14, because the ion product of water Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴.

Can I enter scientific notation?

Yes. Enter concentrations like 1e-3 or 0.001 — both are accepted and parsed in your browser.

pH Calculator

Convert between pH, pOH, [H⁺] and [OH⁻] at 25 °C.

pH calculator

pH measures how acidic or basic a solution is. It is defined as the negative base-10 logarithm of the hydrogen-ion concentration: pH = -log₁₀[H⁺].

Enter any one of [H⁺], pH, [OH⁻], or pOH and this tool returns all four values together, using the 25 °C relationships pH + pOH = 14 and [H⁺][OH⁻] = 1.0 × 10⁻¹⁴. It also labels the solution acidic, neutral, or basic — all computed in your browser.