Free Space Path Loss Calculator

Free space path loss (FSPL) is the attenuation of an RF signal as it propagates through free space with no obstacles, reflections, or absorption. It occurs simply because a radio wave spreads out in all directions as it travels, so the power intercepted by the receiving antenna decreases with the square of the distance. FSPL is expressed in dB and is a fundamental building block of any RF link budget.

FSPL increases with frequency. Every time the frequency doubles, FSPL increases by approximately 6 dB. This is because higher-frequency signals have a shorter wavelength, meaning the effective aperture of a fixed-size receiving antenna captures a smaller fraction of the transmitted power. For example, a 5 GHz WiFi link suffers roughly 20 dB more path loss than a 500 MHz signal over the same distance.

FSPL increases with the square of the distance. Every time the distance doubles, FSPL increases by approximately 6 dB. This is known as the inverse square law. For instance, doubling the range of a wireless link requires the transmit power to be quadrupled (or a 6 dB improvement elsewhere in the link budget) to maintain the same received signal strength.