Calculate pH from hydrogen ion concentration or convert between pH, pOH, [H+], and [OH-] values.
| pH | Example | Nature |
|---|---|---|
| 0-1 | Battery acid, HCl | Strongly acidic |
| 2-3 | Lemon juice, vinegar | Acidic |
| 4-6 | Coffee, milk | Weakly acidic |
| 7 | Pure water | Neutral |
| 8-9 | Baking soda, seawater | Weakly basic |
| 10-12 | Ammonia, bleach | Basic |
| 13-14 | NaOH, drain cleaner | Strongly basic |
At 25 degrees C, the ion product of water Kw = [H+][OH-] = 10^-14. Taking -log of both sides gives pH + pOH = 14.
Yes. Concentrated strong acids can have pH below 0, and concentrated strong bases can exceed 14. The 0-14 range applies to dilute aqueous solutions.
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Open →Enter the hydrogen ion concentration [H⁺] or hydroxide concentration [OH⁻], or the pH/pOH value. The calculator converts between all four forms.
pH = -log₁₀[H⁺]. pOH = -log₁₀[OH⁻]. pH + pOH = 14 (at 25°C). [H⁺] × [OH⁻] = 10⁻¹⁴.
[H⁺] = 1×10⁻³ M: pH = 3 (acidic). [OH⁻] = 1×10⁻² M: pOH = 2, pH = 12 (basic). Pure water: pH = 7 (neutral).
The pH scale is logarithmic — pH 4 is 10× more acidic than pH 5, and 100× more acidic than pH 6. Common pH values: stomach acid ≈ 1.5, lemon juice ≈ 2, blood ≈ 7.4, bleach ≈ 12.5.