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.