You can bound this number from below by the crossing number. The projection of the arcs of two unit circles can cross in at most two points, so $cr(K)\leq C(K)(C(K)-1)$. Also, you ought to be able to bound it quadratically from above by the grid number. If you have a knot presented by a grid diagram, you can represent the knot by a linear number of segments of linear length. Each one of these can be made into a linear number of arcs of unit circles by putting in wiggles. Since grid number is bounded above linearly by crossing number, one obtains inequalities of the form $$\sqrt{cr(K)}\leq C(K)\leq A\cdot cr(K)$$ cr(K)^2$$for some constant A. Notice that the grid number can sometimes be like O(\sqrt{cr(K)}), so I don't expect the upper bound to be sharp. For example, for certain torus knots you'll have C(K)=O(\sqrt{cr(K)}). C(K)=O(cr(K)). 1 You can bound this number from below by the crossing number. The projection of the arcs of two unit circles can cross in at most two points, so cr(K)\leq C(K)(C(K)-1). Also, you ought to be able to bound it quadratically from above by the grid number. If you have a knot presented by a grid diagram, you can represent the knot by a linear number of segments of linear length. Each one of these can be made into a linear number of arcs of unit circles by putting in wiggles. Since grid number is bounded above linearly by crossing number, one obtains inequalities of the form$$ \sqrt{cr(K)}\leq C(K)\leq A\cdot cr(K) for some constant $A$. Notice that the grid number can sometimes be like $O(\sqrt{cr(K)})$, so I don't expect the upper bound to be sharp. For example, for certain torus knots you'll have $C(K)=O(\sqrt{cr(K)})$.