Caution : The accuracy of the calculation of areas from a map depends on many factors (and combination of factors) some of which are :
Do not rely on the result where accuracy is essential.
Area calculation will only produce acceptable answers if the following conditions
Using the Area Calculation
On the Options Menu select the Area Calculation option.
The Area Calculation dialog will be displayed.
Press the Create Track Point Button on the toolbar and draw a track around the perimeter of the area you want calculated by clicking on the map to form a track. As you draw track points the polygon will be filled with hatching. The area will be displayed in the dialog. Select the units for the area.