As per jacob's comment - you can't, http://pomax.github.io/bezierinfo/#circles_cubic http://pomax.github.io/bezierinfo/#circles_cubic covers the "how close do y

As per jacob's comment - you can't, http://pomax.github.io/bezierinfo/#circles_cubic http://pomax.github.io/bezierinfo/#circles_cubic covers the "how close do you want to get" part of circle approximation.