Circle with diameter X and I twist the circle into a figure eight

[LitleBang]

If I had a circle with diameter X and I twist the circle into a figure eight how could I calculate the diameter of one of the resulting approximate circles?

 

[tiny-tim]

Hi LitleBang!

Well, each approximate circle has half the circumference of the original circle,

and if the circumference is halved, then the diameter is … ?

 

[HallsofIvy]

Notice that the total area of the two circles forming the figure 8 is NOT the same as the area of the original circle! But the total circumference is the same as the circumference of the original circle.