Many early units of measurement were based on the human body. For example, a unit of length called the cubit was developed in about 3000 BC in Egypt. The cubit was based on the length from a person's elbow to the tip of the middle finger. Of course, the measurement varied depending on whose arm and finger were used. For this reason the Egyptians created a royal master cubit of black granite, against which all cubit sticks in Egypt were regularly checked. In modern units, the royal cubit was about 21 inches (53 centimeters). The Egyptians could not have built the pyramids without a standard system of measurement.

The ancient people of Babylon and other civilizations of the Middle East developed many units of weights and measures that were handed down to the Western world. Other systems of weights and measures were developed in eastern Asia.

Some of the Roman units of weights and measures are still used today, but not always with the same values. The Romans created the mile to measure long distances. The Roman mile was originally defined as equal to 1,000 paces, or double steps. The Romans used feet also, with 5,000 feet equal to 1 mile. The Romans used a unit of weight called the libra, on which the modern pound is based. The English abbreviation for pound (lb.) means libra.

In Europe during the Middle Ages, many systems of measurement were used. Sometimes the same unit had different meanings depending on what was being measured. Even today, an ounce can mean two different units of weight—the avoirdupois ounce and the troy ounce. The avoirdupois ounce is the common unit, while the troy ounce is used for weighing gold. There are 16 ounces in an avoirdupois pound, but only 12 ounces in a troy pound. The word ounce is also used for the fluid ounce, which is a unit of volume, not weight.

As Great Britain began to dominate world commerce in the 17th century, English weights and measures became the first worldwide system. British colonists took these weights and measures—usually called the British Imperial System—to other continents. Because the British continued to revise their system, however, colonial weights and measures tended to differ slightly. The bushel used in the United States, for example, was smaller than the new bushel adopted in Britain in 1824.

The metric system began to take shape in the 17th century. It was not until the 1790s, however, that the metric system was fully developed. The basic unit is the meter. The metric system is based on multiples of ten. For example, 100 centimeters make up a meter and 1,000 meters make a kilometer. Other units in the metric system include the liter, which measures volume, and the gram, which measures weight. Most countries were using the metric system by the mid–20th century. (See also metric system.)

A modern version of the metric system, the International System of Units (in French, Système Internationale D'unités, or SI), was established in 1960. At an international convention, seven base units were adopted: the meter to measure length, the kilogram to measure mass, the second to measure time, the ampere to measure electric current, the kelvin to measure temperature, the mole to measure amount of substance, and the candela to measure luminosity (light intensity). Other units used in the SI system include the joule to measure energy, the watt to measure power, and the hertz to measure frequency.