pH Calculator
Calculate pH from hydrogen ion concentration, and the pOH and hydroxide concentration.
About pH Calculator
pH is a logarithmic scale, so a change of one unit is a tenfold change in hydrogen ion concentration. The relationship pH + pOH = 14 holds at 25 °C, where the water ionisation constant is 10⁻¹⁴. Because the scale is logarithmic, pH 4 is a hundred times more acidic than pH 6 — not fifty per cent more.
Formula
pH
pH = −log₁₀[H⁺]; pH + pOH = 14 at 25 °C
- [H⁺]
- Hydrogen ion concentration in moles per litre
- log scale
- Each pH unit is a tenfold change in concentration
Worked example
With the default values below, pH Calculator returns pH of 3.0000. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Hydrogen ion concentrationminimum 0 mol/L
- 0.001 mol/L
Results
- pH
- 3.0000
- pOH
- 11.0000
- Hydroxide Ion Concentration
- 0.00000000001000 mol/L
- Classification
- Strongly acidic
- Times More Acidic Than Neutral Water
- 10,000.00
Step by step
- 1Values used
- 2pH
- 3pH= 3.0000
- 4pOH= 11.0000
- 5Hydroxide Ion Concentration= 0.00000000001000 mol/L
- 6Classification= Strongly acidic
- 7Times More Acidic Than Neutral Water= 10,000.00
Assumptions and limits
- The result is derived only from the single input listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 14 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is pH calculated?
pH = −log₁₀[H⁺]; pH + pOH = 14 at 25 °C pH is a logarithmic scale, so a change of one unit is a tenfold change in hydrogen ion concentration. The relationship pH + pOH = 14 holds at 25 °C, where the water ionisation constant is 10⁻¹⁴.
Why does pH matter?
Because the scale is logarithmic, pH 4 is a hundred times more acidic than pH 6 — not fifty per cent more.
What values do I need to enter?
This calculator takes 1 input: Hydrogen ion concentration. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.