Formula Poynting Vector Power density Magnetic field Electric field
$$\boldsymbol{S} ~=~ \frac{1}{\mu_0} \, \left( \boldsymbol{E} ~\times~ \class{violet}{\boldsymbol{B}} \right)$$ $$\boldsymbol{S} ~=~ \frac{1}{\mu_0} \, \left( \boldsymbol{E} ~\times~ \class{violet}{\boldsymbol{B}} \right)$$
Power density
$$ \boldsymbol{S} $$ Unit $$ $$ Poynting vector describes the energy passing through a cross-sectional area per unit time. The Poynting vector is thus a power density.
The cross-sectional area is spanned by \( \boldsymbol{E} \) and \( \boldsymbol{B} \). The Poynting vector is orthogonal to \( \boldsymbol{E} \) and \( \boldsymbol{B} \).
Magnetic field
$$ \class{violet}{\boldsymbol{B}} $$ Unit $$ \mathrm{T} $$ Magnetic flux density determines the strength of the magnetic field and thus the magnitude of the Poynting vector.
Electric field
$$ \boldsymbol{E} $$ Unit $$ \frac{\mathrm V}{\mathrm m} $$ The E-field vector indicates the strength of the electric field. The magnitude of the E-field determines the magnitude of the Poynting vector.
Vacuum permeability
$$ \mu_0 $$ Unit $$ \frac{\mathrm{Vs}}{\mathrm{Am}} = \frac{ \mathrm{kg} \, \mathrm{m} }{ \mathrm{A}^2 \, \mathrm{s}^2 } $$ The vacuum permeability is a physical constant and has the following experimentally determined value:$$ \mu_0 ~=~ 1.256 \, 637 \, 062 \, 12 ~\cdot~ 10^{-6} \, \frac{\mathrm{Vs}}{\mathrm{Am}} $$