ST_Length

For a linear geometry, ST_Length returns the Cartesian length of a 2D projection. The length units are the same as the units in which the coordinates of the input geometry are expressed. The function returns zero (0) for points, multipoints, and areal geometries. When the input is a geometry collection, the function returns the sum of the lengths of the geometries in the collection.

For a geography, ST_Length returns the geodesic length of the 2D projection of an input linear geography computed on the spheroid determined by the SRID. The unit of length is in meters. The function returns zero (0) for points, multipoints, and areal geographies. When the input is a geometry collection, the function returns the sum of the lengths of the geographies in the collection.

Syntax

ST_Length(geo)

Arguments

geo

A value of data type GEOMETRY or GEOGRAPHY, or an expression that evaluates to a GEOMETRY or GEOGRAPHY type.

Return type

DOUBLE PRECISION

If geo is null, then null is returned.

If the SRID value is not found, then an error is returned.

Examples

The following SQL returns the Cartesian length of a multilinestring.

SELECT ST_Length(ST_GeomFromText('MULTILINESTRING((0 0,10 0,0 10),(10 0,20 0,20 10))'));

st_length
--------------------------------
  44.142135623731

The following SQL returns the length of a linestring in a geography.

SELECT ST_Length(ST_GeogFromText('SRID=4326;LINESTRING(5 0,6 0,4 0)'));

 st_length 
------------------
 333958.472379804

The following SQL returns the length of a point in a geography.

SELECT ST_Length(ST_GeogFromText('SRID=4326;POINT(4 5)'));

 st_length 
-----------
 0