pH Calculator
Enter a pH or concentration and get the other acid-base values.
Your numbers
Your results
pH
pH
—
pOH
—
[H⁺] (mol/L)
—
[OH⁻] (mol/L)
—
Nature
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How the pH Calculator works
Choose the quantity you know and enter its value.
pH is the negative base-10 logarithm of the hydrogen ion concentration.
At 25 °C, pH + pOH = 14.
The formula
pH = −log₁₀[H⁺]pH + pOH = 14
Worked example
Using the default values shown in the calculator:
| I know | pH |
|---|---|
| Value | 3.5 |
- pH 3.5 means [H⁺] = 10⁻³·⁵ = 3.162 × 10^-4 mol/L.
- pOH = 14 − 3.5 = 10.5, so [OH⁻] = 3.162 × 10^-11 mol/L.
- The solution is Acidic.
Result:
| pH | 3.500 |
|---|---|
| pOH | 10.500 |
| [H⁺] (mol/L) | 3.162 × 10^-4 |
| [OH⁻] (mol/L) | 3.162 × 10^-11 |
| Nature | Acidic |
Frequently asked questions
Is a pH of 7 always neutral?
Only at 25 °C. At other temperatures the water ion product changes, so neutral pH shifts slightly.
How much more acidic is pH 3 than pH 4?
Ten times. Each pH unit is a factor of 10 in hydrogen ion concentration.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.