STLength (geography Data Type)
Returns the total length of the elements in a geography instance or the geography instances within a GeometryCollection.
If a geography instance is closed, its length is calculated as the total length around the instance; the length of any polygon is its perimeter, and the length of a point is 0. The length of a GeometryCollection is found by calculating the sum of the lengths of all of the geography instances contained within the collection.
The following example creates a LineString instance and uses STLength() to find the length of the instance.
DECLARE @g geography; SET @g = geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656)', 4326); SELECT @g.STLength();