The Terrain Statistics tool measures total length, 2D & 3D area, as well as volume of a selected terrain area.
Zoom out so you can see the space to measure.
Click (Terrain Statistics).
Click the starting point, and then click once for each additional point that makes up the perimeter of the desired area to measure. Double-click to finish.
The measurement information appears centered over the area.
Volume information appears only if you adjusted the elevation of the measured area, for example, by adding a coverage and adjusting its height.
To clear the current measurement, press Esc.
The tool is still active, and you can measure another area.