pH Concentration Calculator
Use this pH concentration calculator to convert between pH and hydrogen-ion concentration [H⁺] in either direction. Pick what you know, enter the value, and it returns pH, [H⁺], pOH and [OH⁻].
Choose whether you know the pH or the [H⁺] concentration, then enter the value to convert.
How to convert between pH and concentration
pH is defined as the negative logarithm of the hydrogen-ion concentration, so the two convert directly:
In water at 25 °C the ion product fixes pH + pOH = 14, which gives the hydroxide side:
Worked example
At pH 3: [H⁺] = 10⁻³ = 0.001 M, pOH = 14 − 3 = 11, and [OH⁻] = 10⁻¹¹ = 1×10⁻¹¹ M. A solution at pH 3 is acidic, with far more H⁺ than OH⁻.
Common pH values for reference
Anchoring a calculated [H⁺] against familiar substances makes the number easier to sanity-check:
| Substance | Typical pH | [H⁺] |
|---|---|---|
| Battery acid | ~0 | ~1 M |
| Stomach acid | ~1.5–2 | ~0.01–0.03 M |
| Lemon juice / vinegar | ~2–3 | ~0.001–0.01 M |
| Black coffee | ~5 | ~1×10⁻⁵ M |
| Pure water (25 °C) | 7 | 1×10⁻⁷ M |
| Seawater | ~8.1 | ~8×10⁻⁹ M |
| Baking soda solution | ~9 | ~1×10⁻⁹ M |
| Household ammonia | ~11 | ~1×10⁻¹¹ M |
| Bleach | ~12.5 | ~3×10⁻¹³ M |
Related tools
To dilute an acid or base to a target strength, use the home dilution calculator. To work in molarity from a mass, see the molarity calculator.
Frequently asked questions
›How do I calculate hydrogen ion concentration from pH?
The hydrogen-ion concentration is [H⁺] = 10^(−pH). For pH 3, [H⁺] = 10⁻³ = 0.001 M. Lower pH means a higher [H⁺] — each pH unit is a tenfold change in concentration.
›How do I find pH from concentration?
Take the negative base-10 logarithm of the hydrogen-ion concentration: pH = −log₁₀[H⁺]. For [H⁺] = 1×10⁻⁵ M, pH = −log₁₀(10⁻⁵) = 5.
›What are pOH and [OH⁻]?
In water at 25 °C, pH + pOH = 14, so pOH = 14 − pH and the hydroxide concentration is [OH⁻] = 10^(−pOH). At pH 3, pOH = 11 and [OH⁻] = 10⁻¹¹ M. This calculator reports all four values at once.
›Is this pH concentration calculator free?
Yes. It runs entirely in your browser, needs no sign-up, and never sends your numbers to a server.
›Why does each pH unit mean a 10× change in concentration?
Because pH is a base-10 logarithmic scale — pH = −log₁₀[H⁺]. Dropping one pH unit means [H⁺] increases tenfold, which is why pH 3 is ten times more acidic than pH 4, not just "one unit more."
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