Divide the lawn into different sections for easy calculation. Whenever possible, ensure that the sections are square or rectangular.
Measure the length and width of each section.
Multiply each section's length by its width to determine the area. For example, if a section of your yard is 15 feet long by 30 feet wide, the area of the section is 450 square feet.
Determine the area of circular sections of your lawn by finding the radius. To find the radius, measure the distance of the area across the center of the circle and divide by two. Multiply the radius by pi, or 3.14, to determine the area. For example, if the circular section has a radius of approximately five feet, multiply five by 3.14 to determine the area, which is 15.7 square feet.
Add the total area of each section together to determine the entire area of the yard.