This RF power density calculator finds how much radio-frequency power falls on a unit area at a given distance from a source. Enter the transmitted power and distance above.
Formula (isotropic source)
S = P ÷ (4π × r²)
For a directional antenna, multiply the transmit power by the antenna gain first.
Example
100 W at 10 m: S = 100 ÷ (4π × 100) = 0.0796 W/m².
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Frequently Asked Questions
How do I calculate RF power density?
Divide the transmitted power by the surface area of a sphere at that range: S = P / (4 pi r squared).
Does antenna gain change power density?
Yes. Multiply the transmit power by the antenna gain to get the effective radiated power in the main beam.
What are the units of power density?
Watts per square meter, or milliwatts per square centimeter for safety limits.