Coaxial Cable Loss Calculator

Estimate total RF loss through a coax feedline from cable type, frequency, and run length, then add connector loss and VSWR mismatch loss. See total attenuation in dB, power delivered to the antenna, the effective radiated fraction, and loss per 100 ft at your frequency for RG58, RG59, RG6, RG213, and LMR series cable.

📡Real Coax Feedline Presets

🔧Feedline Inputs

Coax cable type

Impedance and loss table are set from the cable choice.

Operating frequency (MHz)

Loss scales with the square root of frequency.

Cable run length

One way length from radio to antenna.

Length unit

Meters convert to feet at 3.281 ft per meter.

Transmitter power

Power entering the feedline at the radio.

Power unit

Choose watts or dBm for the input level.

Number of connectors

Count each connector pair along the run.

Loss per connector (dB)

Typical PL259 or N is 0.1 to 0.5 dB each.

Antenna VSWR

1.0 is a perfect match; adds mismatch loss above 1.

Result decimal places

Controls rounding on every result card.

Total cable loss 0 dB matched plus connectors plus mismatch

Power to antenna 0 W delivered at the antenna feed

Effective radiated fraction 0 % percent of input power surviving

Loss per 100 ft 0 dB matched loss at this frequency

🔢Formula Snapshot

dBper100 × L / 100

PoutPin × 10^-dB/10

Γ(SWR-1)/(SWR+1)

ML-10 log(1-Γ^2)

📋Matched Loss per 100 ft by Cable

Coax Type	Impedance	100 MHz	450 MHz	900 MHz	2400 MHz
RG174	50 ohm	8.8 dB	19.0 dB	27.9 dB	47.0 dB
RG58	50 ohm	4.9 dB	10.6 dB	15.6 dB	26.2 dB
RG59	75 ohm	3.4 dB	7.3 dB	10.8 dB	18.1 dB
RG6	75 ohm	1.9 dB	4.3 dB	5.9 dB	9.8 dB
RG8	50 ohm	1.8 dB	3.9 dB	5.7 dB	9.6 dB
RG213	50 ohm	1.9 dB	4.2 dB	6.2 dB	10.4 dB
LMR240	50 ohm	2.2 dB	4.8 dB	6.9 dB	11.6 dB
LMR400	50 ohm	1.5 dB	2.7 dB	3.9 dB	6.8 dB
LMR600	50 ohm	0.9 dB	1.8 dB	2.5 dB	4.4 dB

📡Common Coax by Application and Band

Cable	Impedance	Typical Use	Best Band	Note
RG174	50 ohm	GPS, jumpers	Short runs	Very lossy, keep short
RG58	50 ohm	CB, mobile	HF to VHF	Flexible thin coax
RG59	75 ohm	CCTV, video	VHF baseband	Legacy 75 ohm line
RG6	75 ohm	TV, satellite	UHF to SHF	Low loss for 75 ohm
RG8	50 ohm	Ham base	HF to VHF	Thick low loss coax
RG213	50 ohm	Ham, base	HF to UHF	Rugged double shield
LMR240	50 ohm	Mobile, WiFi	VHF to UHF	RG8X class upgrade
LMR400	50 ohm	WiFi, repeater	UHF to SHF	Low loss workhorse
LMR600	50 ohm	Long tower runs	UHF to SHF	Lowest loss, stiff

📊VSWR to Mismatch Loss

VSWR	Reflection Γ	Reflected Power	Mismatch Loss	Rating
1.0 : 1	0.000	0.0 %	0.00 dB	Perfect
1.2 : 1	0.091	0.8 %	0.04 dB	Excellent
1.5 : 1	0.200	4.0 %	0.18 dB	Good
2.0 : 1	0.333	11.1 %	0.51 dB	Acceptable
2.5 : 1	0.429	18.4 %	0.88 dB	Marginal
3.0 : 1	0.500	25.0 %	1.25 dB	Poor
4.0 : 1	0.600	36.0 %	1.94 dB	Bad
5.0 : 1	0.667	44.4 %	2.55 dB	Very poor

📏Decibel Loss to Power Remaining

Total Loss	Power Remaining	Power Lost	100 W In Gives	Note
0.5 dB	89.1 %	10.9 %	89.1 W	Barely noticed
1 dB	79.4 %	20.6 %	79.4 W	Minor loss
2 dB	63.1 %	36.9 %	63.1 W	Noticeable
3 dB	50.1 %	49.9 %	50.1 W	Half power
6 dB	25.1 %	74.9 %	25.1 W	Quarter power
10 dB	10.0 %	90.0 %	10.0 W	One tenth left
20 dB	1.0 %	99.0 %	1.0 W	Severe loss

⚙Formula Breakdown

Matched loss (dB)Multiply the cable loss per 100 ft at your frequency by the run length in feet divided by 100. For RG58 at 27 MHz that is about 2.5 dB per 100 ft, so 50 ft gives 2.5 × 50 / 100 = 1.27 dB.

Loss vs frequencyCoax attenuation rises with the square root of frequency, so the loss at a new frequency is scaled from a reference by sqrt(f new / f ref). Doubling the frequency raises loss by about 41 percent.

Connector loss (dB)Add the number of connectors times the loss per connector. Four PL259 joints at 0.15 dB each add 4 × 0.15 = 0.6 dB to the total.

Reflection ΓThe reflection coefficient is Γ = (VSWR − 1) / (VSWR + 1). A 1.5 : 1 VSWR gives Γ = 0.5 / 2.5 = 0.20, meaning 4 percent of power is reflected.

Mismatch loss (dB)The extra loss from reflection is ML = −10 × log10(1 − Γ^2). With Γ = 0.20 that is −10 × log10(0.96) = 0.18 dB added to the total.

Total loss (dB)Sum matched loss, connector loss, and mismatch loss. This is the full end to end attenuation from radio to antenna feedpoint.

Power out (W)Power at the antenna is Pin × 10^(−total dB / 10). With 100 W in and 3 dB total, Pout = 100 × 10^(−0.3) = 50.1 W.

Power out (dBm)If input is in dBm, simply subtract: Pout dBm = Pin dBm − total dB. A 43 dBm input through 3 dB of loss leaves 40 dBm at the antenna.

💡Coax Feedline Tips

Match the cable to the band: Thin RG58 loses roughly 10 dB per 100 ft at 450 MHz, which throws away nearly 90 percent of your power over a long run. Switching to LMR400 drops that to about 2.7 dB per 100 ft, keeping over half the power. For any UHF run past 50 ft, budget for low loss coax rather than a longer piece of RG58.

Keep VSWR under 1.5 : 1: A 1.5 : 1 match reflects only 4 percent of power and adds about 0.18 dB of mismatch loss, which is negligible next to cable loss. Above 2.0 : 1 the mismatch adds over 0.5 dB and can stress a transmitter. Tune the antenna first, then judge the feedline, since a bad match wastes power on top of normal cable attenuation.

What good is having an antenna tuned for best gain if you strangle the signal as soon as it gets out of your radio? Cable is what diminishes the signal. The antenna does its job; the cable weaken it. Coaxial cable turns the transmitter’s power into heat with every foot of length. The longer the cable, the more loss; the higher the frequency, the greater the loss. Your investment in coaxial cable result in no range at all so you’re simply paying for something you’ll never get.

Enter your run length, frequency, and cable type into calculator on this page and let numbers do the talking. Time to ditch the long RG58 drop? Upgrade to some beefier cable? Never trust coax to be totaly see-through. There’s still resistance in the center conductor. There’s also still something called dielectric absorbing some of the energy. And both degrade as frequency increases due to skin effect which causes current to crowd toward outside of the conductor. That makes for increased effective resistance proportional to square root of frequency. What works fine on HF might be wasting most of your signal at UHF frequencies. For example, a thin run of RG58 will lose roughly 5 dB/100 feet at 100 MHz increasing to more than 10 dB/100 feet by 450 MHz. Ten decibels equals one tenth of your power getting through. Ouch! It is a brutal signal-loss tax.

How to Stop Losing Radio Signal in Your Cable

Matched loss is the core of the calculation. Matched loss = (loss/100 x run length)/100 That means take your loss per 100 feet times your run length and divide by 100. Then the tool will look up reference losses for each type of cable at various frequencies. It will then scale those values to match your actual frequency based off that square root relationship. So if you have the loss at 450 MHz, the loss at 900 MHz would of been approximately the 450 MHz value times the square root of two. This method means you don’t need separate tables for each band and the number stays fairly realistic across the HF, VHF, UHF, and microwave bands. It is just a simple application of physics to what you are working with.

The right type of cable makes a huge difference in performance. Video systems requires 75-ohm cables (like RG6), whereas radio stuff works best on 50-ohm ones like LMR400 or RG8. That’s because you want all three parts, antenna, cable and radio. To match impedances so reflections aren’t a problem. But even then, you have normal dielectric and conductor losses on your line. Connector pairs adds some insertion loss (usually.1 to.5 dB each, depending on how they’re installed and what family). This isn’t anything for short runs but for long runs with multiple connectors, it can equal a couple feet of loss. Don’t ignore ’em, just count ’em.

An antenna impedance mismatch happen when an antenna doesn’t match the feedline, reflecting some power back toward the transmitter. How much power does it reflect? The voltage standing wave ratio determines that. For instance, a 1.5 to 1 match results in just 4 percent reflected power and less than 0.2 dB of mismatch loss (trivial). On the other hand, a 3 to 1 match reflects a full quarter of all power and more than 1 dB of loss (that’s what people get wrong). They think the cable is bad but the true culprit is a poorly tuned antenna. The calculator puts this mismatch loss into the total so you can see actual picture from end-to-end.

The instant you read the result cards, you know exactly what’s going on. Total loss sums mismatch, connector, and matched losses into one decibel figure. That loss as a wattage value comes from power to antenna. Then you see the fraction (often the most surprising) of power that survives the trip. You get loss per 100 feet at your specific operating frequency so you can compare cable types before buying. You also gets attenuation that matches your specific operating frequency.

These are real world examples. Pre-sets load with real-world situations you can fiddle with or learn from. There are WiFi runs on LMR400, CB runs on RG58, tower drops on LMR600. They is all filled out for you to show the power delivered depending on the cable selected. Then tweak one value and see what happens if you upgrade from thin coax to lower loss options.

Match the cable grade to the run length and band to minimize loss. You may be surprised at how much power you can save by upgrading from RG58 to LMR400 when feeding a UHF run longer than 50 feet. If your signal isn’t hitting the sky, it’s heating the feedline. Learn to tune your antenna before judging your feedline.