A unit of measurement is an amount used to show how much length, or mass, or volume or other quantities something has. There are many different standards and units used all over the world. One global standard is commonly called the metric system. It is also known as International System of Units, or SI. The kilometre, metre, centimetre, millimetre are some units of length or linear size in this system. While many countries have officially adopted SI, a wide range of traditional units are still used. For example, in the United States the metric system has been legal for trade since 1866 and is widely used in industry and daily life. Some basic measurements such as the gallon, inch, mile, and the pound are still widely used. See US units of measurement.

In metric:

• The unit of volume is the litre which is used for water, petrol (gasoline), and other liquid. A litre is equal to a 10 cm by 10 cm by 10 cm (or a one-decimetre cube). There are approximately 3.79 litres in one U.S. gallon. A millilitre is a 1 cm by 1 cm by 1 cm cube — this is also called "ml" or "cubic centimetre". Cooks often use this measurement. A typical teaspoon is about 5 ml in size.

• The unit of mass is the gram which; on Earth is quite light. On Earth it weighs the same as a 1 millilitre of water at 0 degrees Celsius, the temperature where water freezes or ice melts. A more common measure is the kilogram. This weighs the same as a litre of water — 1000 grams because 10x10x10 = 1000. The metric tonne is 1000 kilograms, a million grams.

• The unit of time is the second. The minute (60 seconds) and hour (60 minutes or 3600 seconds) are larger units. The day is usually said to be 24 hours, but is actually a tiny bit longer. This difference is corrected at the end of every year. A week (7 days) and month are also standards in most places, but there are different calendars. These are not part of metric but are used in finance and other industries that set some standards.

Standards are very important. Each unit is a set size. A distance or length or volume or mass or span of time being measured is described as a certain number of these units. Sometimes prefixes are used to change the size of the numbers in a measurement: 1.95 metres is the same as 195 centimeters.

The imperial units now used mainly in the United States: inch, foot, yard, mile, and the U.S. gallon, smaller than the imperial gallon, about 4.5 litres, which is now not used anywhere much. Some older bottles, jugs and liquid containers are this size. There are 16 fluid ounces in a U.S. pint (473 ml, and as shown above, for cool water this is about 473 grams), but there are also 16 ounces in a pound, a measure of weight that is 454 grams. These are two different measurements with the same name, but even when measuring water, the number of ounces of weight is not the same as the number of fluid ounces.

A unit of measurement that applies to money is called a unit of account. This is normally a currency issued by a country—and smaller divisions. For instance, the United States, Canada, Australia, and New Zealand each use dollars which are divided into 100 cents (the value of the dollar in one country is not the same as the value in another country). Other money includes the Euro and Eurocent.

Science, medicine and engineering use larger and smaller units of measurement than these, and talk about them more exactly. For instance the difference between mass and force due to gravity matters more in these fields.

Physics

قياسات | পরিমাপ | Metrologia | Messung | Metrología | Measurement | Mezuro | Métrologie | metrologia | Mensura | Meettechnieken | 測定 | Pomiar | Measurement | Đo lường