Nearly everything done to a yard relies on knowing the area involved. From seeding to fertilizing to topdressing to any other application procedure, the amount of product needed is based on the square foot measurement of the lawn. The complexity of measuring the lawn rises with the number of twists, turns, angles and curves within the lawn. By dividing the lawn into simple blocks, calculating the area becomes an exercise in elementary school geometry, and a little addition.
Sketch the lawn area, omitting hardscape features like sidewalks, patios and driveways. The sketch need not be to scale, but should include relatively accurate representations of all corners and curves. Within each section of the sketch, pencil in the largest possible rectangle.
Measure the length and width of each rectangular section.
Multiply the length by the width of each section and write the results in a column.
Divide all the areas that did not fit into one of the rectangular sections into triangles. This process involves a certain amount of approximation, but unless the lawn includes very large radius curves, the results will be accurate enough for most applications.
Measure one long side of each triangular remainder.
Measure the maximum height of the triangle, perpendicular to the first side measured. Note that this is not always the short side of the triangle. The height measurement must be taken square to the base measurement.
Multiply each triangular section base by its height and divide by 2. For example, a triangular sliver along a property line that was outside a rectangular area might be 50 feet long and 5 feet wide at its widest point (measured square to the 50-foot side). That triangle is 125 square feet (50 times 5 divided by 2).
Add each triangular section to the column of results from the rectangles.
Total the column, giving you the square footage of the yard.