What does pH measure?
How acidic or basic a solution is, from the hydrogen-ion concentration, on a 0-14 scale. Low pH = acidic, 7 = neutral, high = basic.
// chemistry › Acids & Bases
pH Calculator
Calculate pH = −log[H⁺] and classify acidity, with symbol legend and real-world examples.
\text{pH} = -\log[H^+]
Frequently asked questions
Why is the scale logarithmic?
Because hydrogen-ion concentrations span a huge range. Each whole pH unit is a tenfold change - pH 4 is ten times more acidic than pH 5.
Where does pH matter day to day?
Blood (must stay near 7.4), stomach acid, soil for plants, pools, shampoo, food and brewing. It is one of the most-measured quantities anywhere.
How does the example give pH 3?
[H⁺] = 10⁻³, and −log(10⁻³) = 3. A thousandth of a mole of H⁺ per litre is acidic, like orange juice.
How do pH and pOH relate?
In water, pH + pOH = 14. So pH 3 means pOH 11. That is why neutral is pH 7 - exactly half of 14, where H⁺ and OH⁻ are equal.