 This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed.  Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end. This 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. In the physical sciences and engineering, the word "length" is typically used synonymously with "distance", with symbol l or L. Look up Length in Wiktionary, the free dictionary. ...
Wikipedia does not have an article with this exact name. ...
Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Webbased project to create a free content dictionary, available in over 150 languages. ...
2dimensional renderings (ie. ...
Height is the measurement of distance between a specified point and a corresponding plane of reference. ...
Distance is a numerical description of how far apart objects are at any given moment in time. ...
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, length is a fundamental unit, from which other units are derived. Area is a physical quantity expressing the size of a part of a surface. ...
The volume of a solid object is the threedimensional concept of how much space it occupies, often quantified numerically. ...
A set of fundamental units is a set of units for physical quantities from which every other unit can be generated. ...
Units of length
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. Distance is a numerical description of how far apart objects are at any given moment in time. ...
The former Weights and Measures office in Middlesex, England. ...
Various meters Measurement is an observation that reduces an uncertainty expressed as a quantity. ...
In the International System of Units (SI), the basic unit of length is the metre and is now defined in terms of the speed of light. The centimetre and the kilometre, derived from the metre, are also commonly used units. In the English or Imperial system of units, commonly used units of length are the inch, the foot, the yard, and the mile. â€œSIâ€ redirects here. ...
The SI system of units defines seven SI base units: physical units defined by an operational definition. ...
â€¹ The template below (Unit of length) is being considered for deletion. ...
â€œLightspeedâ€ redirects here. ...
The Imperial units are an irregularly standardized system of units that have been used in the United Kingdom and its former colonies, including the Commonwealth countries. ...
An inch (plural: inches; symbol or abbreviation: in or, sometimes, â€³  a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ...
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, â€² â€“ a prime) is a unit of length, in a number of different systems, including English units, Imperial units, and United States customary units. ...
A yard (abbreviation: yd) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. ...
â€œMilesâ€ redirects here. ...
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 lightyear, and the parsec. For other uses, see Astronomy (disambiguation). ...
The astronomical unit (AU or au or a. ...
A lightyear, symbol ly, is the distance light travels in one year: exactly 9. ...
A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ...
Units used to denote microscopically small distances, as in chemistry, include the micron and the ångström. For other uses, see Chemistry (disambiguation). ...
An Ã¥ngstrÃ¶m or aangstroem (the official transliteration), or angstrom (symbol Ã…) is a nonSI unit of length that is internationally recognized, equal to 0. ...
Length of moving rods While the length of a resting rod can be measured by direct comparison with a measuring rod, this comparison cannot be performed while the rod is moving. In this case we define its moving length as the distance between its two endpoints at a given instance. Image File history File links Broom_icon. ...
If the world lines of the two endpoints of the rod expressed in the coordinates of an inertial reference frame are In physics, the world line of an object is the unique path of that object as it travels through 4dimensional spacetime. ...

and 
 ,
then the length of the rod in this reference frame at the instance is 
Since in special relativity the relation of simultaneity depends on the chosen frame of reference, the length of moving rods also depends. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ...
The relativity of simultaneity is the dependence of the notion of simultaneity on the observer. ...
See also 