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File:Height demonstration
A cuboid demonstrating the dimensions length, width, and height

In geometric measurements, length most commonly refers to the longest dimension of an object.[1]

In certain contexts, the term "length" is reserved for a certain dimension of an object along which the length is measured. For example it is possible to cut a length of a wire which is shorter than wire thickness. Another example is FET transistors, in which the channel width may be larger than channel length.

Length may be distinguished from height, which is vertical extent, and width or breadth, which are the distance from side to side, measuring across the object at right angles to the length.

Length is a measure of one dimension, whereas area is a measure of two dimensions (length squared) and volume is a measure of three dimensions (length cubed). In most systems of measurement, the unit of length is a fundamental unit, from which other units are defined.



[2] Measurement has been important ever since man settled from his nomadic lifestyle and started using building materials; occupying land and trading with his neighbours. As society has become more technologically oriented much higher accuracies of measurement are required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging.

One of the oldest units of length measurement used in the ancient world was the 'cubit' which was the length of the arm from the tip of the finger to the elbow. This could then be subdivided into shorter units like the foot, hand (which at 4 inches is still used today for expressing the height of horses) or finger, or added together to make longer units like the stride. The cubit could vary considerably due to the different sizes of people. As early as the middle of the tenth century it is believed that the Saxon king Edgar kept a "yardstick" at Winchester as the official standard of measurement. A traditional tale tells the story of Henry I (1100–1135) who decreed that the yard should be "the distance from the tip of the King's nose to the end of his outstretched thumb".


In the physical sciences and engineering, when one speaks of "units of length", the word "length" is synonymous with "distance". There are several units that are used to measure length. Units of length may be based on lengths of human body parts, the distance travelled in a number of paces, the distance between landmarks or places on the Earth, or arbitrarily on the length of some fixed object.

In the International System of Units (SI), the basic unit of length is the meter and is now defined in terms of the speed of light. The centimeter and the kilometer, derived from the meter, are also commonly used units. In U.S. customary units, English or Imperial system of units, commonly used units of length are the inch, the foot, the yard, and the mile.

Units used to denote distances in the vastness of space, as in astronomy, are much longer than those typically used on Earth and include the astronomical unit, the light-year, and the parsec.

Units used to denote microscopically small distances, as in chemistry, include the micron and the ångström.

See also




Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary



Most common English words: France « London « save « #579: length » play » remained » bear


Old English lengþu





length (plural lengths)

  1. The measurement of distance along the longest dimension of an object.
  2. duration
    • Robert Frost
      Happiness makes up in height for what it lacks in length.
  3. (horse racing) The length of a horse, used to indicate the distance between horses at the end of a race.
  4. (mathematics) Distance between the two ends of a line segment.
  5. (cricket) The distance down the pitch that the ball bounces on its way to the batsman.
  6. (figuratively): total extent
    The length of a book
  7. part of something that's long, a physical piece of something
    A length of rope

Derived terms


Simple English

Simple English Wiktionary has the word meaning for:

Length is a property of a thing that can be measured. The length of something is the distance between two ends of the thing. Short means of small length. Long means of much length. Short and long are opposites. Length is usually the longer side of measurement.



  • A line has one size measurement. This one measurement is the length.
  • A circle's length is called its circumference.
  • A rectangle has two measurements that show its size. These two measurements are the length and the width of the rectangle.
  • The length and width of a square are the same.
  • A box has three measurements that show its size. These three measurements are the length, the width and the depth of the box.
  • The big measurement of a person or a tree standing up is not called length, but height. The big measurement of a tree that fell down is the tree's length.

Distance Examples

  • The distance from the front of the bus to the back of the bus is 30 meters. The bus is said to be 30 meters in length.
  • A piece of wood is 10 meters by 10 cm by 15 cm. The piece of wood is 10 meters in length.

Length of Time

Length is also a property of time. An amount of time has a length.

Time Example

John sits down at one o'clock, or 1h. John waits until three o'clock, or 3h. John stands up at three o'clock, or 3h. John was sitting for 2 hours. The length of time John was sitting was two hours.


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