Last updated: November 19, 2025
Hydrogen ion concentration calculator explained
pH is the negative log base 10 of the hydrogen ion activity. This calculator inverts that definition so you can enter pH or pOH and instantly obtain the corresponding hydrogen ion concentration {hydrogen_ion_concentration}. It also reports {poh} using the 25 deg C relationship .
Use it to translate meter readings into molar concentrations, sanity-check lab reports, or figure out whether a solution is acidic or basic in quantitative terms.
How the conversion works
By definition,
In dilute aqueous solutions at 25 deg C, because . The calculator keeps both expressions synced so you only change one field.
Units and conversions
| Quantity | Units | Notes |
|---|---|---|
| mol/L | Concentration or activity of hydronium. | |
| dimensionless | Typically ranges from 0 to 14 for aqueous systems. | |
| dimensionless | Complements pH via at 25 deg C. |
Worked examples
- Meter reading to [H]
pH = 3.25.
The calculator also reports .
- Concentration to pH
If :
Therefore , showing the solution is mildly basic.
Tips and pitfalls
- The shortcut assumes 25 deg C; use only at that temperature or adjust using .
- Report in mol/L unless you are working with activities; units cancel in the log.
- Avoid rounding intermediate values aggressively; log and antilog operations magnify rounding error.
- For concentrated acids or bases, account for activity coefficients instead of plain molarity to get accurate pH.