pH Calculator

At 25 °C in dilute aqueous solution, pH = −log₁₀[H₃O⁺], pOH = −log₁₀[OH⁻] and pH + pOH = 14. Enter any one of these four quantities to calculate the other three.

The concentration-based formulas assume ideal dilute behaviour and use K_w = 1.0 × 10⁻¹⁴ at 25 °C. In concentrated solutions or when high accuracy is needed, activities rather than bare concentrations are required, and K_w changes with temperature.