pH is a number that tells you how acidic or basic a liquid is. Scientists measure pH on a scale from 0 to 14. Pure water sits right in the middle at 7, which is called neutral. Numbers below 7 mean something is acidic, like lemon juice (around 2) or vinegar (around 3). Numbers above 7 mean something is basic (also called alkaline), like baking soda dissolved in water (around 9) or bleach (around 13).

The “p” is often said to stand for “power” and the “H” represents hydrogen, a tiny particle that helps determine whether something is acidic or basic. The more hydrogen ions floating around in a liquid, the more acidic it is and the lower its pH number.

Understanding pH matters in many situations. Farmers test soil pH because different plants grow best in different conditions: blueberries love acidic soil while asparagus prefers basic soil. Pool owners test water pH to keep it safe and comfortable for swimmers. Your own body carefully controls blood pH around 7.4, and scientists study ocean pH because it affects sea creatures like coral.

The pH scale is logarithmic, meaning each whole number represents a tenfold change. Something with pH 3 is ten times more acidic than something with pH 4, and one hundred times more acidic than pH 5.