In physics, magnetic tension is a restoring force with units of force density that acts to straighten bent magnetic field lines. In SI units, the force density ${\displaystyle \mathbf {f} _{T}}$ exerted perpendicular to a magnetic field ${\displaystyle \mathbf {B} }$ can be expressed as

${\displaystyle \mathbf {f} _{T}={\frac {\left(\mathbf {B} \cdot \nabla \right)\mathbf {B} }{\mu _{0}}}}$

where ${\displaystyle \mu _{0}}$ is the vacuum permeability.

Magnetic tension forces also rely on vector current densities and their interaction with the magnetic field. Plotting magnetic tension along adjacent field lines can give a picture as to their divergence and convergence with respect to each other as well as current densities.

Magnetic tension is analogous to the restoring force of rubber bands.