🔬 pH Calculator
Enter an ion concentration and choose whether it’s H+ or OH- to calculate pH and pOH.
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mol/L
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What This Calculator Does
This calculator converts a hydrogen ion ([H⁺]) or hydroxide ion ([OH⁻]) concentration into pH and pOH, the standard scales chemists use to describe how acidic or basic an aqueous solution is.
The Formula
pH is defined as pH = −log₁₀[H⁺], where [H⁺] is the hydrogen ion concentration in moles per liter. Similarly, pOH = −log₁₀[OH⁻]. At 25°C, pH and pOH always add up to 14, so once you know one you can find the other with pH + pOH = 14.
A Few Notes
- A pH of 7 is neutral, values below 7 are acidic, and values above 7 are basic (alkaline).
- This calculation assumes standard conditions (25°C / 298 K), where the ion-product constant of water (Kw) equals 1.0 × 10⁻¹⁴.
- This tool is provided for general educational and reference purposes, not as a substitute for calibrated laboratory pH measurement.
Last reviewed August 2026