A pH calculator finds the pH of a solution from its hydrogen ion concentration, or converts between pH, pOH, [H⁺] and [OH⁻]. It also handles weak acids and bases using their dissociation constants, making it a handy tool for chemistry homework and lab work.
The core formulas are pH = −log[H⁺], pOH = −log[OH⁻] and pH + pOH = 14 at 25°C. For a strong acid like 0.01 M HCl, which dissociates completely, [H⁺] = 0.01 M and pH = 2. For a strong base like 0.001 M NaOH, [OH⁻] = 0.001 M, pOH = 3 and pH = 11.
Weak acids only partly dissociate, so you need the acid dissociation constant, Ka. For a weak acid with concentration C, [H⁺] ≈ √(Ka × C) when dissociation is small. For 0.1 M acetic acid (Ka ≈ 1.8 × 10⁻⁵), [H⁺] ≈ √(1.8 × 10⁻⁶) ≈ 1.34 × 10⁻³ M, so pH ≈ 2.87. Buffers use the Henderson-Hasselbalch equation: pH = pKa + log([A⁻] ÷ [HA]).
Tips: the pH scale is logarithmic, so a pH of 3 is ten times more acidic than a pH of 4. Use significant figures correctly: the number of decimal places in pH equals the number of significant figures in the concentration. Remember that the value of 14 for pH + pOH applies at 25°C.
Why use an online pH Calculator: it saves time, avoids simple arithmetic mistakes and shows each step, so you can check your homework, plan a project or make a decision with confidence. Bookmark the page so it’s ready the next time you need it.
Tips for getting accurate results from the pH Calculator: double-check that every input uses the right units, enter numbers without commas or symbols, and run the calculation a second time with a quick estimate in your head to confirm the answer looks reasonable.
Learn more on Wikipedia’s pH article. Find stoichiometry, net ionic equation and percent yield calculators on Minedit.