To calculate land area, divide the plot into simple shapes such as triangles, rectangles, parallelograms, circles and half-circles. When calculating the land area for a plot with irregular edges, it is often necessary to split the area into very small pieces. Measure the sides of each shape; for circles, measure the radius. Calculate the area of each shape, and add the results together to get the total land area.
To calculate the area of squares, rectangles and parallelograms, multiply the length times the width. To calculate the area of a circle, multiply pi by the radius squared. For triangles, multiply the base by the height, and divide the result by two. For oval areas, multiply the length by the width, and multiply the result by 0.8.
For areas of land without a scale drawing, take physical measurements. Mark the corners of the plot with ranging poles. Connect them with strings to mark the exterior of the plot. Measure each side, and make a scale drawing. Divide the drawing into standard shapes. Use poles and string to mark each shape on the plot. Measure the sides of each shape, add the dimensions to the drawing, and use the numbers to calculate the area.