About this tool
pH measures the acidity of an aqueous solution. The scale runs 0 (very acidic) to 14 (very basic), with 7 being neutral at 25 °C.
Formula
pH = −log₁₀[H⁺]
Worked example
[H⁺] = 1×10⁻⁷ mol/L → pH = 7 (neutral). [H⁺] = 1×10⁻³ → pH = 3 (acidic).
Notes
Each pH unit represents a 10× change in [H⁺]. pH < 0 and pH > 14 are possible in concentrated strong acids/bases but are rare in everyday chemistry.