The Biot-Savart Law gives the magnetic field ($d\vec{B}$) due to a steady current element $Id\vec{l}$ at a point with position vector $\vec{r}$: $d\vec{B}=\frac{{\mu }_0}{4\pi }\frac{I(d\vec{l}\times \hat{r})}{r^2}$

• In magnitude: $dB=\frac{{\mu }_0}{4\pi }\frac{Idl\sin \theta }{r^2}$
• $\theta$ is the angle between the current element ($Idl$) and the position vector ($\vec{r}$) from the element to the point of observation.