Draw a simple sketch of the roundabout.
Measure the dimensions of the roundabout. If you only want to measure the circle itself, you will need to measure the width of the circle, which is known as the diameter. If you want to measure accompanying areas, such as the beginnings of the roads that branch off from the circle, measure the length and width of these areas as well. You may have some triangular sections between the circle and the roads. Measure the height and base of any triangular portion.
Write in the measurements on your sketch as you make them.
Calculate the area of the roundabout circle itself by first dividing the diameter by 2 to get the radius. Then multiply the radius times itself, which is known as squaring. Finally, multiply the squared radius times pi, which is equal to 3.14.
Figure the area of adjacent areas if you are including them in the total area of the roundabout. For rectangles, multiply the length times the width. For triangles, multiply the base times the height and divide by 2. Add these areas to the circular area for the total area of the roundabout.