International System of Units

The International System of Units (or the "metric system") is a set of standards used all over the world to measure how big or small or heavy something is. It tells us how much a thing weighs and how big or small it is. It can help us compare things from different places, even if they are from different countries. To measure something, you first decide what kind of unit you would like to use. Then you measure it using that unit. Some common units are meters for length, grams for weight and liters for capacity. A meter is about the same as three feet, a gram is about the same as half an ounce and a liter is about the same as a quart.