Hydrogen Ion Concentration Calculator
Enter a pH value to find the hydrogen ion concentration [H⁺] in mol/L — or enter a molar concentration and get pH — along with pOH, [OH⁻], and acid/base classification.
Input type
Neutral
- 1
[H⁺] concentration
[H⁺] = 10^(−7) = 0Each pH unit increase means [H⁺] is ten times lower. - 2
pOH
pOH = 14 − 7 = 7 - 3
pH
pH = 7 = 7
How does this calculator work?
pH = −log₁₀([H⁺]). At 25 °C, pOH = 14 − pH and [OH⁻] = 10^(−pOH). pH < 7 is acidic, = 7 is neutral, > 7 is basic. Enter pH to get concentration, or concentration to get pH.
Formula
How this is calculated
pH is defined as the negative base-10 logarithm of the molar hydrogen ion concentration: pH = −log₁₀([H⁺]). Because the scale is logarithmic, a drop of one pH unit corresponds to a tenfold increase in [H⁺]. At 25 °C, the ion product of water is Kw = [H⁺][OH⁻] = 10⁻¹⁴, placing neutral water at pH 7 ([H⁺] = 10⁻⁷ mol/L). Acidic solutions have pH below 7; basic (alkaline) solutions are above 7.
Since pH + pOH = 14 at 25 °C, knowing either quantity immediately gives the other. The hydroxide concentration [OH⁻] = 10^(−pOH) = Kw/[H⁺]. This calculator handles both directions: enter pH to get [H⁺], or enter a measured molar concentration to get pH and all derived values.
The constant pKw = 14 applies strictly at 25 °C. At 37 °C (body temperature), Kw increases and the neutral point shifts to approximately pH 6.81. This calculator uses 25 °C as the standard reference temperature.
Frequently asked questions
Pure water at 25 °C has [H⁺] = 10⁻⁷ mol/L = 0.0000001 mol/L, giving pH = 7. This is the neutral point because [H⁺] = [OH⁻].
Yes — very concentrated strong acids can have negative pH (e.g. 12 M HCl gives approximately pH −1.1), and concentrated strong bases exceed pH 14. The 0–14 range covers most practical aqueous solutions but is not a strict physical limit.
[H⁺] = 10^(−3) = 0.001 mol/L = 1 × 10⁻³ mol/L. Each integer step up in pH means [H⁺] is ten times lower.
TG we-Calculate Editorial Team. (2026). Hydrogen Ion Concentration Calculator [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/hydrogen-ion-concentration-calculator
TG we-Calculate Editorial Team. "Hydrogen Ion Concentration Calculator." TG we-Calculate. 2026. https://we-calculate.com/calculator/hydrogen-ion-concentration-calculator.
TG we-Calculate Editorial Team, "Hydrogen Ion Concentration Calculator," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/hydrogen-ion-concentration-calculator
@misc{wecalculate_hydrogen_ion_concentration_calculator, title = {Hydrogen Ion Concentration Calculator}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/hydrogen-ion-concentration-calculator}}, year = {2026}, note = {TG we-Calculate} }
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