I have implemented GeoDjango using postgis.
Here is my model:
geometria = models.PolygonField(srid=4326, null=True)
If you are dealing with large areas on the map, you should set
geometria = models.PolygonField(srid=4326, null=True, geography=True)
As mentioned in geodjango's documentation https://docs.djangoproject.com/en/dev/ref/contrib/gis/model-api/#geography
Geography Type In PostGIS 1.5, the geography type was introduced -- it provides native support for spatial features represented with geographic coordinates (e.g., WGS84 longitude/latitude).  Unlike the plane used by a geometry type, the geography type uses a spherical representation of its data. Distance and measurement operations performed on a geography column automatically employ great circle arc calculations and return linear units. In other words, when ST_Distance is called on two geographies, a value in meters is returned (as opposed to degrees if called on a geometry column in WGS84).
If you do not have
geography=True, we are storing things as plain geometries, we will need to do conversion from
square degrees (the floating point result you are getting) into a unit of measure you prefer because we cannot calculate area from geographic coordinates. We can instead add a helper method which is in a projected coordinate space to do the transformation:
def get_acres(self): """ Returns the area in acres. """ # Convert our geographic polygons (in WGS84) # into a local projection for New York (here EPSG:32118) self.polygon.transform(32118) meters_sq = self.polygon.area.sq_m acres = meters_sq * 0.000247105381 # meters^2 to acres return acres
Which projection we use depends on the extent of the data, and how accurate we need the results: here I've illustrated with a specific projection for part of New York, but if your data isn't particularly accurate, you could easily substitute a global projection or just use a simple formula.