pH Calculator
pH and pOH from hydrogen ion concentration — or concentration from pH.
Quick answer
- Formula: pH = −log₁₀[H⁺]; pOH = 14 − pH; [H⁺] = 10^(−pH) (at 25 °C)
- Worked example — pH: 7.000 (full example below).
pH Calculator
| pH | 7.000 |
| pOH | 7.000 |
| [H⁺] concentration | 0.0000001000 mol/L |
| [H⁺] (scientific notation) | 1.000e-7 mol/L |
| Solution is | Neutral |
Pure water with [H⁺] = 1×10⁻⁷ mol/L has pH 7.00 and pOH 7.00 — neutral.
![Diagram: how the pH Calculator works — you enter Mode, Hydrogen ion concentration [H⁺], pH value; it applies the formula pH = −log₁₀[H⁺]; pOH = 14 − pH; [H⁺] = 10^(−pH) (at 25 °C); and the worked example gives pH: 7.000.](/calc-images/ph-calculator.svg)
pH measures acidity on a logarithmic scale: pH = −log₁₀[H⁺], where [H⁺] is the hydrogen ion concentration in mol/L. Each pH unit is a tenfold change in concentration.
Enter a concentration (scientific notation such as 1e-7 is fine) to get pH, pOH and whether the solution is acidic, neutral or alkaline at 25 °C, where pH + pOH = 14. Reverse mode converts a pH value back to [H⁺].
The formula
Worked example
Pure water with [H⁺] = 1×10⁻⁷ mol/L has pH 7.00 and pOH 7.00 — neutral.
![Worked example for the pH Calculator: with Mode pH from [H⁺] concentration, Hydrogen ion concentration [H⁺] 0, pH value 7, the result is pH: 7.000; pOH: 7.000.](/calc-images/ph-calculator-example.svg)
The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.
Frequently asked questions
Why is the pH scale logarithmic?
Concentrations span many orders of magnitude (from over 1 mol/L to below 10⁻¹⁴). A log scale compresses that range into the familiar 0–14 window; one pH unit always means a factor of ten.
Can pH be below 0 or above 14?
Yes, for very concentrated strong acids or bases — for example 10 mol/L HCl has pH ≈ −1. The 0–14 range simply covers most dilute aqueous solutions at 25 °C.
Category: Science calculators
Sources & methodology
This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.
Content last reviewed by CalcHub Editorial.
Embed this calculator on your site
Free to use with attribution — paste the snippet below and the calculator appears on your page, with a link back to CalcHub.
Related calculators
Molarity Calculator
Concentration in mol/L from moles and volume — or solve for either one.
Dilution Calculator
M₁V₁ = M₂V₂: solve any one dilution value from the other three.
Logarithm Calculator
Logarithm of a number in base 10, e, 2 or any custom base.
Scientific Notation Calculator
Convert a decimal number into scientific notation: coefficient × 10^exponent.