Area of a circle = Pi x radius squared, or 3.14 times half the diameter squared.

In your case the radius is the distance from the long flat wall to the outer edge of the curved wall in feet.

so half a circle is [(3.14 x width) x (3.14 x width)]/2 or more simply (Pi*r^2)/2

thanks for your quick reply.

I'm trying to figure out how many yards of concrete I will need for my steps. They're half circle shape. The bottom step is has a radius of 15.7, and sticks out 5' foot from the house. The top step has a radius of 9.42, and sticks out 3' from the house. Both steps are 8" tall.

We may need a drawing of this. The part that sticks out away from the house, is this rectangle shaped? So it would be a half circle next to a rectangle?

check my math.

rectangles:

8/12*(9.42*2)*3 = 62.8ftcu

and 8/12*(15.7*2)*5 =104.7ftcu

plus your two semicircles

0.5 *(3.14159*9.42*9.42)*8/12= 258.1 ftcu

and

0.5 *(3.14159*15.7*15.7)*8/12= 92.9

ftcu

I got 518 cubic ft.

There should be 9 cubict feet in a yard. so I get 57.6

Best to check the math. No warranty.

maybe there are 27cubic feet in a cubic yard. cr*p.

19.18. That sounds a little better