About the pH Calculator
What is the pH Calculator?
pH measures how acidic or basic a solution is, on a scale where 7 is neutral at 25 °C. This pH calculator works from [H⁺] or [OH⁻], from the concentration of a strong acid or base, or from a weak acid's concentration and Ka.
For weak acids it solves the equilibrium exactly instead of using the square-root approximation.
How to use the pH Calculator
- From (sample: Hydrogen ion concentration [H⁺])
- Concentration (mol/L) (sample: 0.001)
- Acid Dissociation Constant Ka (weak acid only) (sample: 0)
- Press Calculate pH (results also refresh as you type). The result card shows the pH, along with pOH, [H⁺], [OH⁻] and Solution is.
Formula used
pH = −log₁₀[H⁺]; pH + pOH = 14
- Weak acid = [H⁺] = (−Ka + √(Ka² + 4 Ka C)) ÷ 2
- Strong base = [H⁺] = 10⁻¹⁴ ÷ [OH⁻]
Assumes 25 °C and dilute solutions, where activity ≈ concentration.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| From | Hydrogen ion concentration [H⁺] |
| Concentration (mol/L) | 0.001 |
| Acid Dissociation Constant Ka (weak acid only) | 0 |
| Result | Value |
|---|---|
| pH | 3 |
| pOH | 11 |
| [H⁺] | 0.001 mol/L |
| [OH⁻] | 0.00000000001 mol/L |
| Solution is | Acidic |
| Assumption | At 25 °C, where Kw = 1.0 × 10⁻¹⁴ |
Tips for using the pH Calculator
- Each pH unit is a tenfold change in hydrogen ion concentration.
- Drinking water in India should be between pH 6.5 and 8.5 (IS 10500).