How is pH calculated?

pH is the negative base-10 logarithm of the hydrogen ion concentration in mol/L, so pH = -log10[H⁺]. A pH below 7 is acidic, 7 is neutral, and above 7 is basic at 25 °C.

How are pH and pOH related?

At 25 °C, pH + pOH = 14, because the ion product of water Kw = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴.

Can I enter scientific notation?

Yes. Enter concentrations like 1e-3 or 0.001 — both are accepted and parsed in your browser.

How do I find [H⁺] from a pH value?

Take the inverse log: [H⁺] = 10^(−pH). A pH of 3 gives [H⁺] = 10⁻³ = 0.001 mol/L. Choose the "from pH" mode and the tool does this for you.

How do I get [OH⁻] from [H⁺]?

Use Kw: [OH⁻] = 1.0 × 10⁻¹⁴ ÷ [H⁺]. If [H⁺] is 10⁻³, then [OH⁻] is 10⁻¹⁴ ÷ 10⁻³ = 10⁻¹¹ mol/L.

Why is pure water neutral at pH 7?

In pure water at 25 °C, [H⁺] equals [OH⁻] at 1.0 × 10⁻⁷ mol/L, so pH = pOH = 7. Neither ion dominates, which is the definition of neutral.

Does the temperature matter?

Yes. Kw and therefore the neutral pH change with temperature. This tool assumes 25 °C, where Kw = 1.0 × 10⁻¹⁴ and neutral pH is 7; at higher temperatures neutral pH is slightly below 7.

pH Calculator — Gera Tools

pH calculator

pH measures how acidic or basic a solution is, on a scale where 7 is neutral at 25 °C. This tool converts freely between pH, pOH, the hydrogen-ion concentration [H⁺] and the hydroxide-ion concentration [OH⁻] — enter any one and it returns the other three, plus an acidic / neutral / basic label.

How it works

The conversions rest on three relationships at 25 °C:

pH  = −log10[H⁺]          [H⁺] = 10^(−pH)
pOH = −log10[OH⁻]         pH + pOH = 14
Kw  = [H⁺][OH⁻] = 1.0 × 10⁻¹⁴

Whatever you enter is converted to [H⁺] first, then pH, pOH and [OH⁻] follow. Concentrations accept scientific notation such as 1e-3. A pH below 7 is labelled acidic, exactly 7 neutral, and above 7 basic.

Example

Enter [H⁺] = 1 × 10⁻³ mol/L:

pH = −log10(10⁻³) = 3 (acidic)
pOH = 14 − 3 = 11
[OH⁻] = 10⁻¹⁴ ÷ 10⁻³ = 1 × 10⁻¹¹ mol/L

[H⁺] (mol/L)	pH	pOH	[OH⁻] (mol/L)
1×10⁻³	3	11	1×10⁻¹¹
1×10⁻⁷	7	7	1×10⁻⁷
1×10⁻¹¹	11	3	1×10⁻³

Everything is computed in your browser — nothing is uploaded.