About this calculator
Free pH Calculator - Calculate pH from hydrogen ion concentration or vice versa.
How to use
Enter your values in the fields above and click Calculate to see your results. Click Clear to reset all fields.
Frequently Asked Questions
What conditions do these calculations assume?
Standard chemistry calculations assume standard temperature and pressure (STP: 0°C, 1 atm) or standard conditions (25°C, 1 atm) unless you specify otherwise. Reaction rates, equilibria, and solubility all change significantly with temperature, so results may not apply directly to non-standard conditions.
How do significant figures affect my answer?
Your answer can only be as precise as your least-precise input. Count the significant figures in each input and round your final answer to match the fewest sig figs among them. For most homework and lab report purposes, 3-4 significant figures are appropriate.
What's the difference between molarity and molality?
Molarity (M) is moles of solute per liter of solution — it changes with temperature because liquid volumes expand. Molality (m) is moles of solute per kilogram of solvent — it's temperature-independent. Use molality for colligative property calculations; molarity for most stoichiometry and lab work.
Why is my calculated pH different from my measured pH?
Calculated pH assumes ideal behavior and complete dissociation for strong acids/bases. Real solutions deviate from ideality, especially at high concentrations. Activity coefficients, ionic strength, temperature effects, and instrument calibration errors all create gaps between calculated and measured pH values.