STArea (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Returns the total surface area of a geometry instance.
Syntax
.STArea ( )
Return Types
SQL Server return type: float
CLR return type: SqlDouble
Remarks
STArea() returns 0 if a geometry instance contains only 0- and 1-dimensional figures, or if it is empty. STArea() returns NULL if the geometry instance has not been initialized.
Examples
A. Computing the area of a Polygon instance
The following example creates a Polygon``geometry instance and computes the area of the polygon.
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('POLYGON((0 0, 3 0, 3 3, 0 3, 0 0),(2 2, 2 1, 1 1, 1 2, 2 2))', 0);
SELECT @g.STArea();
B. Computing the area of a CurvePolygon instance
The following example computes the area of a CurvePolygon instance.
DECLARE @g geometry;
SET @g = geometry::Parse('CURVEPOLYGON(CIRCULARSTRING(0 2, 2 0, 4 2, 4 2, 0 2))');
SELECT @g.STArea() AS Area;