pH Calculator
By Santaji GadepatilinUpdated October 27, 2026
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Acidic
Type in any field to change it. Press × on a value to calculate that field instead.
How to use this calculator
Enter any one of pH, [H⁺], pOH or [OH⁻] — the rest are calculated (at 25 °C). For a strong acid like HCl, [H⁺] equals the acid concentration.
Formulas
pH = −log₁₀[H⁺] pOH = 14 − pH [OH⁻] = 10−pOH
Worked example
pH 4.5:
- [H⁺] = 10⁻⁴·⁵ = 3.16e-05 mol/L
- pOH = 9.5, [OH⁻] = 3.16e-10 mol/L
pH of everyday substances
| Substance | pH |
|---|---|
| Battery acid | ~0–1 |
| Lemon juice | ~2 |
| Coffee | ~5 |
| Pure water | 7 |
| Sea water | ~8 |
| Baking soda solution | ~9 |
| Household bleach | ~12–13 |
Each pH unit is a tenfold change: pH 3 is ten times more acidic than pH 4.
Frequently asked questions
What is pH?
A measure of acidity — the negative base-10 logarithm of hydrogen ion concentration. pH 7 is neutral at 25 °C.
How do I calculate pH from H⁺ concentration?
pH = −log₁₀[H⁺]. A concentration of 1 × 10⁻³ mol/L gives pH 3.
Why does pH + pOH = 14?
Because water's ion product Kw is 1.0 × 10⁻¹⁴ at 25 °C. At other temperatures the sum changes slightly.