Coaxial Cable Loss Calculator

Calculate signal loss through coaxial cable in dB given frequency, length, and cable type. Supports RG-58, RG-59, RG-6, LMR-240/400/600 and custom attenuation coefficients.

Calculator Electronics Updated Apr 18, 2026
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How to Use
  1. Pick a cable type (RG-58, LMR-400, etc.) or enter custom attenuation at a reference frequency.
  2. Enter the operating frequency and cable length.
  3. The tool computes loss in dB, power fraction retained, and voltage ratio at the far end.
  4. Loss scales as √frequency for most coax — double the frequency, loss increases ~40%.
Input
Hz (kHz, MHz, GHz OK)
m (or ft)
W
Presets
Loss vs. Frequency
Total Loss
—dB
Power Retained
—%
Loss per 100m
—dB
Output Power
—W

Show Work

Enter values to calculate loss.

Formulas

Frequency Scaling
α(f) = α₀ × √(f / f₀)
Loss in dB/100m scales with √frequency.
Total Loss
L = α × (length / 100)
Linear with cable length.
Power Fraction
P_out / P_in = 10−L/10
Converting from dB back to linear power.
Voltage Ratio
V_out / V_in = 10−L/20
Voltage uses 20 instead of 10 in denominator.
3 dB Rule
−3 dB = ½ power
Every 3 dB cuts signal power in half.
Meters ↔ Feet
1 m = 3.281 ft
Multiply ft by 0.3048 to get meters.

History of Coaxial Cable

Oliver Heaviside patented the basic coaxial cable concept in 1880, describing a center conductor inside a grounded outer sheath with the space filled by a dielectric. The first practical coaxial cable for long-distance telephony was developed at AT&T\'s Bell Labs in the 1920s; Lloyd Espenschied and Herman Affel filed the seminal patent in 1929. The first transatlantic telephone cable (TAT-1, 1956) used coaxial construction to carry 36 voice channels between Newfoundland and Scotland.

RG (Radio Guide) designations date to World War II Army-Navy specifications. RG-58 (50 Ω, thin) and RG-8 (50 Ω, thick) became the amateur radio and low-power RF standards, while RG-59 and RG-6 (75 Ω) dominated TV distribution. Times Microwave\'s LMR series (1990s) brought foam-dielectric low-loss cable to the consumer market at prices competitive with old RG-213. Modern premium options include CNT-400, Andrew Heliax hardline, and various semirigid cables for instrumentation.

The √frequency loss scaling in this calculator comes from two physical effects: skin-effect resistance (Rac ∝ √f) in the copper conductors, and dielectric loss tangent in the polyethylene or foam dielectric. At 1 MHz, skin effect dominates; above a few GHz, dielectric loss takes over. The √f approximation holds well from HF through low-microwave frequencies — above ~10 GHz, waveguide replaces coax because the loss becomes prohibitive.

About This Calculator

Pick a common cable type or enter a custom attenuation coefficient at a reference frequency, then enter operating frequency (Hz, kHz, MHz, or GHz) and length (meters or feet). The tool computes total loss in dB, power-retained percentage, per-100m loss for design reference, and output power given your transmit power.

Defaults use manufacturer-spec nominal values at 20 °C, dry, no bending. Real cable losses can be 10–30% higher when hot, wet, bent sharp, or aged. Add 0.1–0.3 dB per connector for realistic link budgets. Everything runs client-side; no values leave your browser.

Frequently Asked Questions

Why does frequency matter so much?

Skin effect causes most of the current to flow in a thin layer near the conductor surface at high frequencies. As frequency rises, the effective cross-section shrinks and resistance rises. Dielectric losses also increase with frequency. Together they cause loss to scale roughly as √f.

Which cable should I use?

Short runs (<10m) to indoor antennas: RG-58 or RG-6 are fine. Long runs or higher frequencies: LMR-400 or better. The rule of thumb: every doubling of length = 3dB loss in power, or 6dB in voltage ratio.

What is 3dB loss?

3dB = half the power. A 3dB loss means only 50% of your transmitter power reaches the antenna. 6dB = 25%, 10dB = 10%, 20dB = 1%. Long coax runs at high frequency can easily lose 10dB or more.

Does impedance mismatch increase loss?

Yes — SWR > 1:1 causes additional loss because some power reflects back from the mismatched load. Well-matched cables (SWR < 1.5) have minimal extra loss beyond the cable's rated attenuation.

Common Use Cases

2m VHF Ham Setup

50ft of LMR-400 at 145 MHz: ~1.1 dB loss. Acceptable. Same run of RG-58: ~4.5 dB — significant.

UHF/Wi-Fi Link

20ft of RG-58 at 2.4 GHz: ~9 dB loss (87% of power gone). Always use thicker, lower-loss cable at GHz frequencies.

FM Broadcast TX

100m of 1/2" hardline at 100 MHz: ~2 dB loss. Essential for broadcast transmitters where every dB costs money.

Satellite TV Downfeed

50ft of RG-6 at 1.5 GHz: ~3 dB loss. RG-6 is purpose-designed for this frequency band.

HF Base Station

30m of RG-213 at 14 MHz: ~0.5 dB loss. HF cables can be long without major impact.

Wi-Fi Antenna Extension

10ft of LMR-240 at 5.8 GHz: ~1.7 dB loss. Any longer and you lose meaningful signal strength.

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