Size is how big or small something is. When you describe the size of your backpack, you're talking about how much space it takes up or how much it can hold. When you compare the size of two pizzas, you're looking at which one is larger.

Size can be measured in different ways depending on what matters most. A basketball player's size usually means height, but a wrestler's size might include both height and weight. A computer file's size refers to how much digital storage space it occupies. An elephant is enormous in size compared to a mouse, but the size of an atom is far too tiny to see even with your eyes.

People use size in many everyday situations. Clothing comes in different sizes (small, medium, large, or numbered sizes like 10 or 12). When you're picking teams for a game, you might try to make sure they're roughly the same size, meaning about the same number of players. Scientists study everything from the size of galaxies to the size of molecules.

As a verb, size can mean to measure or sort by size, like when a store sizes shoes or a machine sizes fruit. The phrase cut down to size means to humble someone who's acting too proud or important. And when someone sizes up a situation, they're carefully evaluating it, like a chess player studying the board before making a move.