The Area Tool lets you measure the area, total perimeter length or specific segment lengths of an object when you hover over it.
As well as individual objects, you can measure multiple objects' areas by selecting them. The tool will also calculate object areas with holes in them, without the hole being included in the measurement.
The tool also lets you scale your document or the currently selected artboard by either setting a scale factor (e.g., 1:100, 1cm:1km) or by scaling to a known distance (e.g., 10 meters) on a currently measured object dimension.
The following settings can be adjusted from the context toolbar: