Magnitude of the resultant couple:
For non-parallel forces also the location of the line of action of resultant may be determined by utilizing R × d = ∑ M _{o} .
The magnitude of the resultant couple is specified by
and
cos α_{ x} = ∑ M_{x} / M, cos α_{ y }=∑ M_{y}/ M, cos α_{ z }= ∑ M_{z}/ M
where ∑ M _{x }, ∑ M _{y} and ∑ M _{z} are the algebraic sums of the moments of the couples of the system around x, y and z axes, respectively. The angles α_{x}, α_{y} and α_{z} are the angles, the vector representing the couple M makes along with x, y and z axes, respectively.
In particular case of concurrent forces, M = 0.