pH Calculator
A solution with [H⁺] = 0.001 mol/L has a pH of 3, from pH = −log₁₀[H⁺]; it is acidic.
For a strong acid, [H⁺] = concentration × number of acidic H (e.g. 0.01 M HCl → 0.01).
3
- pOH = 14 − pH
- 11
- [H⁺]
- 0.001 mol/L
- [OH⁻]
- 1 × 10⁻¹¹ mol/L
- Solution is
- acidic
Step-by-step solution
- pH = −log₁₀[H⁺] = −log₁₀(0.001)
- pH = 3
- pOH = 14 − 3 = 11
pH Formula
pH = −log₁₀[H⁺], pH + pOH = 14
[H⁺] hydrogen-ion concentration (mol/L), [OH⁻] hydroxide concentration; pKw = 14 at 25 °C
Worked Example
A solution with [H⁺] = 0.001 mol/L (0.001 M HCl):
- pH = −log₁₀[H⁺] = −log₁₀(0.001)
- pH = 3
- pOH = 14 − 3 = 11
[H⁺]: 0.001 mol/L · [OH⁻]: 1 × 10⁻¹¹ mol/L · Solution is: acidic
A logarithmic scale
Each pH unit is a factor of 10 in [H⁺]: pH 3 is ten times more acidic than pH 4 and a thousand times more than pH 6.
Frequently asked questions
What is the pH of a strong base?
Use [OH⁻]: 0.01 M NaOH gives pOH 2 and pH 12. For Ca(OH)₂, double the concentration (two OH⁻ per formula unit).
Does this work for weak acids?
Only if you know [H⁺]. For a weak acid of concentration C, [H⁺] ≈ √(Ka × C) when it ionises little; enter that value.
Is neutral always pH 7?
Only at 25 °C. Water’s Kw rises with temperature, so pure water at 50 °C has pH about 6.6 while still neutral.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). pH Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/ph-calculator/
IEEE
Scientific Converters, "pH Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/ph-calculator/