How to calculate flux density in a toroidal CT that has an electrical line pass through the center?
You probably want to avoid the Biot-Savart rule and instead determine the magnetic field strength, H. This can then be converted to flux density (B) by multiplying H by \$\mu_0\mu_r\$.

\$\mu_0 \times\mu_r\$ is the magnetic permeability of your toroid material.

H is the ampere-turns per meter applied where metres are the mean length of the magnetic field and for a toroid that is approximately the length round the toroid. Amps is amps and turns is turns. For a CT this converts to just amps because you have a single turn.