pH Calculator
Use this pH calculator to move between pH, pOH, hydrogen-ion concentration, hydroxide concentration, and weak-acid Ka relationships in one place.
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Run the calculator.
What This pH Calculator Helps You Do
This page packages the most common pH conversions together, so you can move between logarithmic values and ion concentrations without keeping separate formulas open.
The added weak-acid mode also covers a common chemistry use case where you know Ka and concentration but still need the actual pH of the solution.
How to Calculate pH Calculator
- Choose the input form: Use H+, OH-, pH, or weak-acid Ka with concentration depending on the information you already know.
- Let the calculator convert related values: The page reports pH along with linked aqueous quantities such as pOH and the complementary ion concentration.
- Interpret acidity: Read whether the solution is acidic, neutral, or basic under the standard room-temperature assumption.
pH Calculator Formula
| Variable | Meaning | Unit |
|---|---|---|
| [H+] | Hydrogen ion concentration | mol/L |
| [OH-] | Hydroxide ion concentration | mol/L |
| pH | Negative base-10 log of hydrogen ion concentration | unitless |
| pOH | Negative base-10 log of hydroxide ion concentration | unitless |
| Ka | Acid dissociation constant | unitless |
| c | Initial weak-acid concentration | mol/L |
Use the worked examples below to check how the formula behaves with real values. If the result looks unexpected, verify the unit assumptions and the meaning of each variable before interpreting the answer.
Worked Examples
- [H+]: 0.0001 mol/L
Result: pH = 4.0000
A hydrogen-ion concentration of 10^-4 mol/L is mildly acidic.
- Ka: 1.8e-5
- Acid concentration: 0.1 mol/L
Result: pH ≈ 2.8753
Weak-acid mode solves the dissociation relation before converting to pH.
How to Interpret Your Results
| Range | Meaning | Action |
|---|---|---|
| < 7 | Acidic solution | Lower pH means higher hydrogen-ion concentration. |
| 7 | Neutral solution | At room temperature, neutral water sits near pH 7. |
| > 7 | Basic solution | Higher pH means lower hydrogen-ion concentration and higher hydroxide concentration. |
Frequently Asked Questions
References
Last reviewed: March 2026