Attenuation Calculator

Calculate distance-based path loss, medium attenuation, and remaining signal strength for radio, sound, or optical links.

Signal attenuation inputs

Model logarithmic spreading loss and optional linear medium loss between two distances.

Initial Signal Strength (dBm)

Initial Distance (m)

Final Distance (m)

Frequency (MHz)

Path Loss Exponent

Medium Loss (dB/m)

About signal attenuation

Attenuation is the reduction in signal level as energy travels through space or a material. Radio waves spread over a larger area, sound loses energy to air and surfaces, and light is absorbed or scattered by optical media. Engineers usually express these ratios in decibels because logarithms turn repeated multiplication into convenient addition. A loss of 20 dB means the power ratio has fallen by a factor of one hundred, regardless of the absolute transmitter level. This calculator reports free-space path loss from distance in meters and frequency in megahertz. Internally it converts megahertz to hertz and applies 20 times the base-ten logarithm of distance plus 20 times the logarithm of frequency in hertz, minus 147.55 dB. It also calculates the change in level between a reference and final distance with the log-distance model. That term is ten times the path-loss exponent times the logarithm of the distance ratio. An exponent of two represents ideal free-space spreading, while obstructed environments commonly use larger empirical values. The optional medium coefficient adds a linear number of decibels for every meter traveled beyond the reference point. Set it to zero when spreading is the only effect you want to model. Initial signal strength is entered in dBm, an absolute power level referenced to one milliwatt. Attenuation is measured in dB, a relative ratio. Subtracting the calculated relative loss from the starting dBm level gives the final estimated dBm level. Keeping these units distinct prevents a common mistake: dBm levels can be negative, while a positive attenuation value indicates a reduction. The absolute free-space path-loss result and the relative signal estimate answer different questions. Free-space loss describes an ideal unobstructed path from a theoretical isotropic source at the stated frequency and final distance. The final signal calculation treats the entered initial signal as a measurement at the initial distance, then applies the modeled change over the remaining path. Frequency cancels from that relative free-space ratio, but it remains essential to the absolute path-loss value. The result is an engineering estimate, not a site survey or complete link budget. Antenna gains, connector losses, cable loss, transmitter variation, receiver sensitivity, terrain, weather, walls, and polarization may all matter. Use a realistic reference distance, frequency, and environmental exponent, then compare the final level with the receiver threshold. Measurements at several positions remain the best way to calibrate a dependable propagation model.

Attenuation examples

The examples separate ideal spreading from additional absorption in the propagation medium.

Signal path	Calculated result	Interpretation
30 dBm, 1 m to 10 m, 2,400 MHz, exponent 2, 0 dB/m	FSPL 60.054 dB; relative loss 20 dB; 10 dBm final	A tenfold free-space distance increase adds 20 dB of relative path loss.
-20 dBm, 2 m to 20 m, 900 MHz, exponent 3, 0.2 dB/m	FSPL 57.555 dB; relative loss 33.6 dB; -53.6 dBm final	Thirty decibels come from spreading and 3.6 dB from the lossy medium.
0 dBm, 5 m to 50 m, 100 MHz, exponent 2.5, 0.1 dB/m	FSPL 46.429 dB; relative loss 29.5 dB; -29.5 dBm final	The absolute loss depends on frequency, while the measured-level change uses the distance ratio.

How to use the attenuation calculator

Enter the measured or specified signal strength at the reference position.
Provide the positive reference distance and a final distance that is at least as large.
Enter the signal frequency, choose an environmental path-loss exponent, and add any linear medium loss per meter.
Select Calculate Attenuation to view spreading loss, total attenuation, and final signal level.

Attenuation calculator FAQ

What is the difference between dB and dBm?

A decibel is a relative gain or loss ratio, while dBm is an absolute power level referenced to one milliwatt. You can subtract a dB loss from a dBm level to obtain a new dBm level.

Which path loss exponent should I use?

Use two for ideal unobstructed free-space spreading. Real indoor, urban, or obstructed environments often require an empirical value from roughly two to five based on measurements.

Why can final signal strength be negative?

Negative dBm values simply represent powers below one milliwatt and are normal for received signals. A more negative value is weaker than a less negative value.

Does the calculator include antenna gain?

No, it models only distance and optional medium attenuation from the entered starting level. Add antenna gain, cable loss, connector loss, and other link-budget terms separately.

Can this model be used for sound or light?

Yes, the logarithmic and linear attenuation pattern can represent many waves. Ensure that the starting level, coefficient, and interpretation of the final unit are appropriate for the physical system.