pH Calculator
Calculate pH from hydrogen ion concentration, or compute [H⁺] and [OH⁻] from a known pH.
What is pH Calculator?
The pH calculator computes pH = −log₁₀[H⁺]. The pH scale goes from 0 (very acidic) to 14 (very basic), with 7 as neutral.
Formula
pH = −log₁₀[H⁺]. Each whole pH unit = 10× change in [H⁺]. [OH⁻] = 10⁻¹⁴ / [H⁺].
Worked example
[H⁺] = 10⁻⁴ mol/L → pH = 4 (acidic). pH 7 → [H⁺] = 10⁻⁷ mol/L (neutral water).
How to use this calculator
- Pick conversion direction.
- Enter value.
- Solution is classified as acidic, neutral, or basic.
Frequently asked questions
Why is pH logarithmic?
Hydrogen concentrations vary across 14 orders of magnitude. The log scale compresses this into manageable numbers (0–14).
Real-world pH values?
Stomach acid: 1.5–3.5. Lemon juice: 2. Vinegar: 2.4. Coffee: 5. Pure water: 7. Blood: 7.4. Seawater: 8. Soap: 9–10. Bleach: 12.5. Drain cleaner: 13–14.
Can pH go below 0 or above 14?
Yes — the 0–14 range is an approximation for typical aqueous solutions. Concentrated acids can have pH below 0; concentrated bases above 14.
How is pH measured?
pH meter (electrode), litmus paper (rough), or chemical indicators that change color at specific pH values. pH meters give 0.01 precision; paper gives 0.5–1 unit.