Chemistry acid-base calculator

pH Calculator

Calculate pH, pOH, hydrogen-ion concentration, and hydroxide-ion concentration from any known acid-base measurement.

Enter acid-base data

Calculate pH

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Select the acid-base value already known.

Enter the known pH value.

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Calculator guide

How this calculator works

pH Calculator determines the acidity or alkalinity of a solution by calculating hydrogen ion concentration. It helps chemistry students, researchers, and laboratory professionals analyze acids, bases, and solution properties accurately.

Formula explanation

The pH calculator determines acidity or alkalinity by analyzing hydrogen ion concentration in a solution.

Formula

pH = -log₁₀[H⁺]

Worked example

Example: Lower pH values indicate higher hydrogen ion concentration and stronger acidity.

Assumptions

  • Concentration values are entered using compatible units.
  • The solution behavior follows standard acid-base relationships.
  • Measurements represent the actual chemical solution accurately.

Examples

  • Example: Hydrogen ion concentration can be converted into a pH value to determine solution acidity.
  • Example: Chemists use pH calculations to prepare solutions and monitor chemical reactions.

Common mistakes

  • Using incorrect concentration units.
  • Confusing pH and pOH.
  • Ignoring logarithmic scale behavior.

Variables

  • Hydrogen ion concentration
  • Hydroxide ion concentration
  • pH value
  • pOH value
  • Acid or base strength

Limitations

  • Accuracy depends on correct concentration measurements.
  • Complex solutions may require additional chemical equilibrium calculations.

Scientific references

  • OpenStax Chemistry: Acids and Bases
  • NIST Chemistry Reference Data
  • Scientific laboratory acid-base analysis guidelines

Content review

Reviewed by: ScienceCalcHub Chemistry Review Team | Last reviewed: 2026-08-30

Applications

  • Acid-base analysis
  • Laboratory solution testing
  • Chemical education
  • Environmental chemistry

Frequently asked questions

How is pH calculated?

pH is calculated by taking the negative logarithm of the hydrogen ion concentration in a solution.

What does a pH value represent?

A pH value represents the acidity or alkalinity of a solution based on its hydrogen ion concentration.

What is the difference between pH and pOH?

pH measures hydrogen ion concentration, while pOH measures hydroxide ion concentration in a solution.

Accuracy and transparency

Created and maintained by our editorial team

This chemistry calculator is maintained by the ScienceCalcHub Editorial Team. Its calculation logic is tested with representative inputs, while the supporting guidance is checked for formula clarity, units, assumptions, and common mistakes.

Written by
ScienceCalcHub Editorial Team
Reviewed by
ScienceCalcHub Scientific Review Team
Review standard
Formula accuracy, units, examples, and educational clarity

Learn more about our formula-review and correction process, explore our calculation methodology, or view our scientific references.

  • Calculation logic tested
  • Variables and units explained
  • Assumptions stated clearly
  • Corrections handled transparently

Formula

How pH is calculated

pH =−log₁₀[H⁺]

The pH scale describes the concentration of hydrogen ions in an aqueous solution. Because the scale is logarithmic, a change of one pH unit represents a tenfold change in hydrogen-ion concentration.

Acid-base relationships

pH, pOH, H⁺, and OH⁻ formulas

  • pH = −log₁₀[H⁺]
  • pOH = −log₁₀[OH⁻]
  • pH + pOH = 14 at 25 °C
  • [H⁺] = 10⁻ᵖᴴ
  • [OH⁻] = 10⁻ᵖᴼᴴ
  • [H⁺][OH⁻] = 1 × 10⁻¹⁴at 25 °C

Worked example

Calculate pH from hydrogen-ion concentration

Suppose a solution has a hydrogen-ion concentration of 1 × 10⁻⁵ mol/L.

  1. Use the formula pH = −log₁₀[H⁺].
  2. Substitute the concentration: pH = −log₁₀(1 × 10⁻⁵).
  3. Calculate the logarithm: pH = 5.
  4. Since pH 5 is below 7, the solution is acidic.

pH scale

Acidic, neutral, and basic solutions

  • pH below 7: acidic solution
  • pH equal to 7: neutral solution
  • pH above 7: basic or alkaline solution

The neutral value of 7 and the pH plus pOH relationship of 14 apply specifically to aqueous solutions near 25 °C. Temperature changes the ionization constant of water.

Chemistry guidance

Common pH calculation mistakes

  • Entering ion concentration as a negative value.
  • Forgetting the negative sign in the logarithm formula.
  • Confusing hydrogen-ion concentration with hydroxide-ion concentration.
  • Assuming every pH value must remain between 0 and 14.
  • Applying the pH plus pOH equals 14 relationship without considering temperature.

Related chemistry tools

Use the Molarity Calculator to calculate the molar concentration of a solution.

Use the Dilution Calculator when preparing a lower-concentration solution from a stock solution.

Use the Mass to Moles Calculator to convert between solute mass and amount in moles.

Questions and answers

Calculator FAQ

How is pH calculated?

pH is calculated by taking the negative logarithm of the hydrogen ion concentration in a solution.

What does a pH value represent?

A pH value represents the acidity or alkalinity of a solution based on its hydrogen ion concentration.

What is the difference between pH and pOH?

pH measures hydrogen ion concentration, while pOH measures hydroxide ion concentration in a solution.