Calculating polygon areas and perimeters using QGIS

Question

Using QGIS, if I load a polygon layer and make a new column, how do I fill that column with the area of each polygon and another column with the length of the perimeter of each polygon?

Answer 1

Open the Field Calculator, select the new column and type the following expression

• For area : $area
• For perimeter: $perimeter

Make sure your layer is in a projected coordinate system (not lat/long) and in correct units (i.e. if your layer's projection has 'meters' as units, your area will be square meters).

Note that reprojecting layers on-the-fly does not change the units for area/perimeter calculation, so you have to first reproject using Save as ... with the correct target CRS.

Answer 2

For QGIS versions 2.16 and above (see the Changelog for QGIS 2.16) use the "Add geometry attributes" tool from Vector > Geometry Tools > Add geometry attributes.

You also can use fTools: Vector menu -> Geometry Tools -> Export/Add geometry columns

It updates your layer automatically by adding "AREA" and "PERIMETER" columns.