Math & Everyday
pH Calculator
Convert between pH, pOH, and hydrogen/hydroxide ion concentration.
🔒 Runs entirely in your browser — nothing here is ever uploaded
CalcoTools · pH Calculator · generated 9/1/2026, 2:28:11 PM
About the pH Calculator
Converts between pH, pOH, and hydrogen/hydroxide ion concentration — enter either the pH directly or a hydrogen ion concentration, and get the full picture computed from the standard logarithmic relationships.
100% Free Runs in Your Browser No Sign-Up Required
How to use it
- Choose whether you know the pH or the hydrogen ion concentration [H⁺].
- Enter that value.
- Read the pH, pOH, [H⁺], and [OH⁻], plus whether the solution is acidic, neutral, or basic.
Formula
pH = −log₁₀[H⁺]. [H⁺] = 10^(−pH). pOH = 14 − pH (at 25°C). [OH⁻] = 10^(−pOH).
Worked example
A solution with pH 3: [H⁺] = 1.000×10⁻³ mol/L, pOH = 11, [OH⁻] = 1.000×10⁻¹¹ mol/L — clearly acidic.
Approximate pH of Common Substances
| Substance | pH |
|---|---|
| Battery acid | < 1 |
| Gastric acid | 1.0-1.5 |
| Vinegar | 2-3 |
| Orange juice | 3.3-4.2 |
| Black coffee | ~5 |
| Pure water (25°C) | 7 |
| Seawater | 7.5-8.4 |
| Ammonia | 11.0-11.5 |
| Bleach | 12.5 |
| Lye (drain cleaner) | 14 |
Interpreting your result
The pH + pOH = 14 relationship holds specifically at 25°C. This is a straightforward pH/pOH/concentration conversion tool, not a titration or buffer calculator.
Recommendations
- • Each whole pH unit represents a 10× change in hydrogen ion concentration.
- • pH and pOH always sum to 14 at 25°C.
- • Pure water is neutral (pH 7) only at 25°C.
Frequently asked questions
Hydrogen ion concentrations span many orders of magnitude, so a log scale compresses that range.
Related searches
Sources
- LibreTexts Chemistry — The pH Scale — accessed 2026-08-30
- Wikipedia — pH — accessed 2026-09-01