# Length

In general English usage, **length** (symbols: l, L) is but one particular
instance of distance ï¿½ an object's length is how long the object is ï¿½ but in the
physical sciences and engineering, the word length is in some contexts used
synonymously with "distance". **Height** is vertical distance; **width** (or breadth) is a lateral
distance; an object's width is less than its length.

No one speaks of "the length from here to Alpha Centauri", but rather of "the
distance from here to Alpha Centauri," but when one speaks of distance more
abstractly, one says "A kilometre or a mile, is a unit of length" or "...of
distance", and the two statements are synonymous. Likewise, a mountain might be a mile in height. Length is the metric of one
dimension of space. The metric of space itself is volume, or (length)^{3}.
Length is commonly considered to be one of the fundamental units, meaning that
it cannot be defined in terms of other dimensions.

**See also**

2D | Two-dimensional coordinate system |

3D | Three-dimensional coordinate system |

Angle | Definition of an angle |

Axis | Definition of Cartesian axis |

Cartesian geometry | What is Cartesian geometry? |

Coordinate system | Definition of coordinates |

Curve | Definition of a curve |

Distance | Definition of distance |

Euclidean geometry | What is Euclidean geometry? |

Geometry | Definition of geometry |

Length | Definition of length |

Line | Definition of a line |

Origin | Definition of origin in a Cartesian coordinate system |

Perspective projection | Definition of perspective projection |

Planar homography | Definition of planar homography |

Plane | Definition of a plane |

Point | Definition of a point |

Point (kinematics) | Definition of a point (kinematics) |

Projective geometry | What is projective geometry? |

Segment (kinematics) | Definition of a segment (kinematics) |

Vanishing points | Definition of vanishing points and vanishing lines in perspective projection |

Vector | Definition of a vector |