This Power density calculator allows you to measure the power density from an antenna to a certain distance, by providing the output power and gain values. Generally used in RF and Radar applications, power density is measure of the power in a certain distance from the antenna.
Below is the formula to calculate the power density:
Pd = Po*G/4*π*D2
Pd = Power density in watts/m2
Po = Output power from the antenna in watts (W)
G = Gain of the antenna
D = Distance from the antenna in meters (m)