What is the pH formula?

pH = −log₁₀[H⁺], where [H⁺] is the hydrogen-ion concentration in mol/L. A [H⁺] of 1×10⁻³ mol/L gives pH 3.

How are pH and pOH related?

At 25 °C, pH + pOH = 14, because the ion product of water Kw = [H⁺][OH⁻] = 1×10⁻¹⁴. So pOH = 14 − pH.

What pH is acidic, neutral or basic?

At 25 °C pH below 7 is acidic, exactly 7 is neutral, and above 7 is basic (alkaline). The scale is logarithmic, so each unit is a 10× change in [H⁺].

Does temperature change this?

Yes — Kw and therefore neutral pH shift with temperature. This calculator uses the standard 25 °C value (Kw = 10⁻¹⁴, neutral pH 7).

pH & pOH Calculator

The pH scale measures how acidic or basic a solution is: pH = −log₁₀[H⁺], where [H⁺] is the hydrogen-ion concentration in mol/L. Its partner pOH = −log₁₀[OH⁻] tracks the hydroxide ions, and at 25 °C the two always satisfy pH + pOH = 14 because the ion product of water Kw = [H⁺][OH⁻] = 10⁻¹⁴. Enter any one of the four — pH, pOH, [H⁺] or [OH⁻] — and this calculator returns the other three and labels the solution acidic (pH < 7), neutral (pH = 7) or basic (pH > 7). Concentrations are shown in scientific notation so very small ion amounts stay readable.

—

Input

Value

Neutral

pOH

[H⁺]

1.000e-7 mol/L

[OH⁻]

1.000e-7 mol/L

pH = −log₁₀[H⁺]; pH + pOH = 14 at 25 °C. Each pH unit is a 10× change in hydrogen-ion concentration.

How to use

Choose which quantity you know: pH, pOH, [H⁺] or [OH⁻].
Enter its value (concentrations in mol/L).
Read pH, pOH, both ion concentrations and whether the solution is acidic, neutral or basic.

Frequently asked questions

What is the pH formula?: pH = −log₁₀[H⁺], where [H⁺] is the hydrogen-ion concentration in mol/L. A [H⁺] of 1×10⁻³ mol/L gives pH 3.
How are pH and pOH related?: At 25 °C, pH + pOH = 14, because the ion product of water Kw = [H⁺][OH⁻] = 1×10⁻¹⁴. So pOH = 14 − pH.
What pH is acidic, neutral or basic?: At 25 °C pH below 7 is acidic, exactly 7 is neutral, and above 7 is basic (alkaline). The scale is logarithmic, so each unit is a 10× change in [H⁺].
Does temperature change this?: Yes — Kw and therefore neutral pH shift with temperature. This calculator uses the standard 25 °C value (Kw = 10⁻¹⁴, neutral pH 7).

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