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ST_Length

Calculates the Cartesian length of a LineString or the perimeter of a Polygon.

Syntax​

ST_Length(geometry)

Parameters​

ParameterTypeDescription
geometryGeometryInput geometry

Returns​

TypeDescription
Float64Length (for lines) or perimeter (for polygons)

Examples​

Length of a LineString​

SELECT ST_Length(ST_GeomFromText('LINESTRING(0 0, 3 4)'));
-- Returns: 5.0

Perimeter of a Square​

SELECT ST_Length(ST_GeomFromText('POLYGON((0 0, 4 0, 4 4, 0 4, 0 0))'));
-- Returns: 16.0

Calculate Total Road Length​

SELECT road_type, SUM(ST_Length(geom)) as total_length
FROM roads
GROUP BY road_type;

Find Long LineStrings​

SELECT * FROM rivers
WHERE ST_Length(geom) > 1000;

Notes​

  • Returns 0 for Points
  • For Polygons, returns the perimeter (length of exterior ring plus all interior rings)
  • For MultiLineStrings, returns the sum of all line lengths
  • Length is in the same units as the input geometry coordinates
  • For geographic coordinates, the result is in degrees (not meters)

See Also​