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 | 250 MHz | ~19.8 dB |
| RG-6 coaxial | 1 GHz | ~18 dB |
| RG-6 coaxial | 2.4 GHz | ~27 dB |
| Single-mode fiber | 1310 nm | ~0.35 dB |
| Multimode fiber | 850 nm | ~2.5 dB |
Connector loss: typically 0.1–0.5 dB per connection (coax), 0.2–0.5 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. Cable loss = 18 dB/100 m × 45 m / 100 = 8.1 dB Connector loss = 3 × 0.3 = 0.9 dB Total loss = 9.0 dB
With 9 dB loss and an input signal of 10 mW: P_out = 10 × 10^(−9/10) = 10 × 0.126 = 1.26 mW remaining
Systems with more than 20–25 dB of loss typically require signal amplifiers to maintain quality.