Coax Cable Loss Calculator
Cable type + frequency + length → total RF loss in dB and percent of power surviving the run.
Result
- CableRG-58
- Frequency146 MHz
- Length100 ft
- Loss per 100 ft1.86 dB
- Total loss1.86 dB
- Power surviving65.24%
- 100 W input → output65.2 W
Step-by-step
- Per-100ft loss model: dB = A·√f + B·f = 0.122·√146 + 0.00261·146 = 1.855 dB/100ft.
- Total loss = 1.855 × (100 / 100) = 1.855 dB.
- Power surviving = 10^(−1.855 / 10) = 0.6524 → 65.24%.
How to use this calculator
- Pick the cable type from the list.
- Enter the operating frequency in MHz.
- Enter the run length in feet.
- Read total loss and the fraction of power that reaches the far end.
About this calculator
Coax cable loss has two main mechanisms — conductor loss (skin effect, scales with √f) and dielectric loss (scales linearly with f). At HF (3-30 MHz) conductor loss dominates; at UHF and above (>300 MHz) dielectric loss takes over. The two-parameter A·√f + B·f model used here captures both terms from a single regression against manufacturer datasheets. RG-58 is the lossiest of the common 50 Ω cables at VHF; LMR-400 cuts losses by 2-3x at the same diameter; LMR-600 cuts them again at much higher cost.
What this calculator does
This calculator reports total coax-cable RF power loss in dB given the cable type, operating frequency, and run length, and converts that loss into the percentage of input power that reaches the far end. It uses a two-parameter A·√f + B·f attenuation model fit to manufacturer datasheets — one term captures skin-effect conductor loss, the other captures dielectric loss. The supported cable list covers the common 50 Ω amateur/commercial cables (RG-58, RG-8X, RG-213, LMR-400, LMR-600) and the common 75 Ω TV/satellite cables (RG-6, RG-11).
How it works — the formula
attenuation (dB/100 ft) = A·√f + B·f (f in MHz)
total loss (dB) = (A·√f + B·f) × (length / 100)
power surviving = 10^(−total_loss / 10)Skin-effect (conductor) loss scales as √f because the depth current flows in shrinks with frequency. Dielectric loss scales linearly with f because every cycle dissipates a fixed fraction of stored field energy in the insulator. The A and B coefficients here are extracted from Times Microwave, Belden, and Andrew (Commscope) published per-100-ft attenuation tables across multiple frequencies; the two-term fit is accurate within ~5% from HF through UHF.
Worked examples
- Inputs:
- cable=RG-58, f=146, len=100
- Output:
- Loss ≈ 1.85 dB; 65% power surviving
Borderline acceptable for a 2 m FM rig at a modest installation. Half the length (50 ft) cuts loss in half (~0.93 dB).
- Inputs:
- cable=LMR-400, f=146, len=100
- Output:
- Loss ≈ 0.76 dB; 84% surviving
The same 100 ft of RG-58 would lose ~1.85 dB more.
- Inputs:
- cable=RG-6, f=1500, len=30
- Output:
- Loss ≈ 1.83 dB; 65% surviving
TV/sat is loss-tolerant because LNB gain is high; longer runs typically need RG-11.
When to use this vs other tools
Use this when planning RF feedlines. For audio/DC cabling, voltage-drop math applies instead.
- SWR Calculator
Use to relate forward/reflected power readings — high SWR plus cable loss compounds into more heat in the line.
- Antenna Length
Use to size the antenna feeding into the coax — coax loss tradeoffs depend on the antenna gain and frequency.
- Transmission Line Impedance
Use to verify the cable Z₀ matches the source/load and avoid additional mismatch loss on top of attenuation.
- Decibel Calculator
Use to convert between dB, power ratios, and voltage ratios when totaling link budgets.
Authority note
The A·√f + B·f attenuation model is fit to the published per-100-ft loss tables for each cable. These datasheets are the authoritative reference for cable loss; the model captures their behavior to within a few percent across HF to UHF.
Limitations
- Loss values are nominal — connector mismatches, water ingress, and physical damage add unpredictable extra loss.
- Model is fit through ~6 GHz. Above that, additional dispersion and surface-roughness effects make per-cable measurement essential.
- Temperature effects (~0.4%/°C on conductor resistance) are not modeled; rooftop coax in summer loses a bit more.
- High SWR multiplies effective cable loss because the reflected wave traverses the line twice — the calculator reports matched-line loss only.
For commercial or licensed-transmit installations, verify loss with a network analyzer or wattmeter at both ends rather than relying on the nominal model.