Calculates the area of a surface in the specified units.
SELECT TREAT( Shape AS ST_Polygon ).ST_Area() FROM SpatialShapes WHERE ShapeID = 22
The following returns the area of the poly_geometry column in square miles from the fictional region table.
SELECT name, poly_geometry.ST_Area( 'Statute Mile' ) FROM region
SQL/MM (ISO/IEC 13249-3: 2006) 8.1.2