pH Calculator
Last updated: June 2026
Formula
pH = -log10[H+]. [H+] = 10^(-pH). pOH = 14 - pH. [OH-] = 10^(-pOH).
| pH | Example |
|---|---|
| 0 | Strong acid |
| 1 | Stomach acid |
| 2 | Lemon juice |
| 3 | Vinegar |
| 5 | Coffee |
| 7 | Pure water |
| 8 | Seawater |
| 9 | Baking soda |
| 11 | Ammonia |
| 13 | Bleach |
| 14 | Strong alkaline |
About this calculator
The pH Calculator converts between hydrogen ion concentration, pH, pOH, and hydroxide ion concentration for simple aqueous chemistry examples. It is useful for students learning acids and bases, lab preparation checks, and everyday pH scale interpretation.
pH and pOH formulas
pH is a logarithmic measure of hydrogen ion concentration. At 25 C for simple aqueous solutions, pH and pOH are commonly treated as adding to 14.
- pH = -log10([H+])
- [H+] = 10^(-pH)
- pOH = 14 - pH
- [OH-] = 10^(-pOH)
How to use the pH calculator
- Choose whether to calculate pH from H+ concentration or H+ from pH.
- Enter concentration in mol/L or enter a pH value.
- Review pH, pOH, H+, and OH- results.
- Check whether the result is acidic, neutral, or alkaline.
- Use the pH scale to compare with common substances.
- Remember that pH is logarithmic, not linear.
Worked examples
Neutral water style example
Input: [H+] = 1 x 10^-7 mol/L
Calculation: pH = -log10(1 x 10^-7)
Result: pH 7, neutral in the standard simplified model
Acidic solution
Input: pH = 3
Calculation: [H+] = 10^-3
Result: 0.001 mol/L hydrogen ion concentration
pH scale reference
| pH range | Meaning |
|---|---|
| 0-3 | Strongly acidic |
| 4-6 | Weakly acidic |
| 7 | Neutral in the simplified scale |
| 8-10 | Weakly alkaline |
| 11-14 | Strongly alkaline |
Why pH changes quickly
The pH scale is logarithmic. A change of one pH unit means a tenfold change in hydrogen ion concentration.
Chemistry calculation disclaimer
This calculator is for educational chemistry use. Real solutions can be affected by temperature, activity coefficients, buffers, concentration limits, and measurement calibration.
Frequently asked questions
What does pH measure?
pH measures hydrogen ion concentration on a logarithmic scale.
Is pH 7 always neutral?
pH 7 is treated as neutral in many school examples at 25 C, but temperature and solution chemistry can affect neutrality.
What does acidic mean?
A solution with pH below 7 is usually described as acidic in the simplified scale.
What does alkaline mean?
A solution with pH above 7 is usually described as alkaline or basic.
Can pH be outside 0 to 14?
Yes, concentrated solutions can fall outside that range, although 0-14 is the common teaching scale.
Related calculators
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- Logarithm Calculator
- Ratio Calculator
What does this mean?
This calculator is designed to help you understand the likely number before you make a decision or start an application.
Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.
Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.
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