For a bounded region R in ℝ3 with smooth boundary Ʃ, and for a continuously differentiable vector field F on R,
Here dS = n dS, where S denotes surface area and n is the outward-pointing unit normal. As the divergence divF represents the local expansion/contraction of the field F, then the theorem states that the sum of such expansions equals the flux of F over the boundary Ʃ. See Stokes’ theorem (generalized form).