Cable Signal Loss Calculator
Calculate signal attenuation in dB per 100 ft for coaxial and Ethernet cables by type, length, and frequency.
Covers RG6, RG59, Cat5e, and Cat6.
Signal loss (also called attenuation) is the reduction in signal strength as it travels through a cable, connector, or medium. It is measured in decibels (dB) — a logarithmic unit that allows wide-ranging power ratios to be expressed as manageable numbers.
Signal loss formula: Loss (dB) = Attenuation Rate (dB/m) × Length (m)
Total path loss: Total Loss = Cable Loss + Connector Loss × Number of Connectors + Splice Loss × Number of Splices
Decibel relationship to power: Loss (dB) = 10 × log₁₀(P_in / P_out)
Where:
- P_in = input power (watts or milliwatts)
- P_out = output power at the receiving end
Signal remaining after loss: P_out = P_in × 10^(−Loss/10)
Typical attenuation rates:
| Cable Type | Frequency | Loss (dB/100m) |
|---|---|---|
| Cat5e Ethernet | 100 MHz | ~22 dB |
| Cat6 Ethernet | 100 MHz | ~19.8 dB |
| Cat6 Ethernet | 250 MHz | ~31 dB |
| Cat6a Ethernet | 100 MHz | ~18 dB |
| Cat6a Ethernet | 500 MHz | ~40 dB |
| RG-6 coaxial | 1 GHz | ~18.4 dB |
| RG-6 coaxial | 2.4 GHz | ~28.5 dB |
| Single-mode fiber | 1310 nm | ~0.35 dB |
| Multimode fiber | 850 nm | ~2.5 dB |
Attenuation depends on frequency, and that is the part people forget
The same cable is not equally lossy at every frequency. Conductor loss climbs with the square root of frequency, because of the skin effect: as frequency rises, current crowds into a thinner and thinner outer layer of the copper, and the effective resistance goes up. Quadruple the frequency and you roughly double the loss.
Loss at f ≈ Loss at f_ref × √(f / f_ref)
That is why a Cat6 run rated 19.8 dB per 100 m at 100 MHz measures around 31 dB at 250 MHz, and why RG-6 goes from about 18.4 dB per 100 m at 1 GHz to about 28.5 dB at 2.4 GHz. Published certification figures run a few dB above the square-root estimate at the very top of a cable’s range, because dielectric loss adds a second term that grows in direct proportion to frequency rather than to its square root. For sizing a run, the square root model is close enough. For certifying one, use a tester.
A common mistake is to quote a category’s headline attenuation and then attach it to that category’s maximum rated frequency. Cat6’s 19.8 dB figure is a 100 MHz number, not a 250 MHz one.
Connector loss: typically 0.1 to 0.5 dB per connection (coax), 0.2 to 0.5 dB (fiber).
Worked example: A 75-ohm RG-6 coaxial cable runs 45 meters for a cable TV signal at 1 GHz. There are 3 connectors at 0.3 dB each. RG-6 is quoted at 5.6 dB per 100 ft at 1 GHz, which is 18.4 dB per 100 m. Cable loss = 18.4 dB/100 m × 45 m / 100 = 8.3 dB Connector loss = 3 × 0.3 = 0.9 dB Total loss = 9.2 dB
With 9.2 dB loss and an input signal of 10 mW: P_out = 10 × 10^(−9.2/10) = 10 × 0.120 = 1.20 mW remaining, or 12% of what went in
Systems with more than 20–25 dB of loss typically require signal amplifiers to maintain quality.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.