Enter your signal's Frequency, Distance, and antenna gains (GTx and GRx) to calculate Free Space Path Loss — how much signal power is lost as your transmission travels through open air. You'll also get the signal's Wavelength and Basic Path Loss without antenna gains factored in.
Free Space Path Loss
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Wavelength
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Basic Path Loss (no antenna gains)
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Free space path loss (FSPL) is the attenuation of radio signal strength as it travels through free space (vacuum) between transmitting and receiving antennas. It represents the natural spreading of electromagnetic waves over distance, even in ideal conditions with no obstacles or interference.
FSPL is calculated using the formula: FSPL (dB) = 20 log₁₀(d) + 20 log₁₀(f) + 20 log₁₀(4π/c) - GTx - GRx, where d is distance, f is frequency, c is speed of light, and GTx/GRx are antenna gains. Our calculator handles all unit conversions automatically.
Free space path loss increases with the square of the distance. Doubling the distance results in 6 dB additional loss. This relationship follows the inverse square law of electromagnetic radiation.
Free space path loss is caused by the natural spreading of electromagnetic waves as they propagate through space. As the signal travels farther from the transmitter, the same amount of power is distributed over a larger spherical area, reducing the power density at the receiver.
Higher frequencies experience greater free space path loss. Doubling the frequency increases path loss by 6 dB. This is why higher frequency bands like 5G millimeter waves have shorter range compared to lower frequency bands.
Antenna gain increases signal strength in a specific direction and reduces the overall path loss calculation. A higher gain antenna (measured in dBi) can partially compensate for free space path loss by focusing the signal energy more directionally.
No, real-world conditions include additional losses from atmospheric absorption, rain fade, obstacles, and multipath interference. Free space path loss represents the theoretical minimum loss in perfect vacuum conditions with clear line-of-sight.
Antenna gains (GTx for transmitter, GRx for receiver) are subtracted from the basic path loss calculation. Positive gain values reduce total path loss, while negative values (antenna losses) increase it. Use 0 dBi for isotropic antennas.