Calculator · Feed Line

Coax Loss Estimator

Estimate signal loss for common coax types at ham radio frequencies. See how much power reaches your antenna — and how much is wasted as heat in the feed line.

Calculate Feed Line Loss

Coax Type

Frequency (MHz)

Coax Length (feet)

Transmit Power (Watts)

Coax Loss at Common Frequencies (dB per 100 feet)

Coax Type	50 MHz	146 MHz	440 MHz	1296 MHz
RG-58	2.5	4.9	9.0	18.0
RG-8X	1.5	2.8	5.2	11.0
LMR-240	1.2	2.1	3.9	7.4
LMR-400	0.65	1.15	2.1	4.5
RG-213/RG-8	1.3	2.4	4.7	10.5

Source: Times Microwave and Belden published loss data. Values are typical; actual loss varies with connector quality, age, and moisture.

When does coax type actually matter?

For runs under 25 feet at VHF: any decent coax is fine. For runs over 50 feet, or at 440 MHz and above, coax quality matters significantly. A 100-foot run of RG-58 at 440 MHz loses 9 dB — that is 87% of your power wasted before it reaches the antenna. The same run in LMR-400 loses only 2.1 dB (38% loss). At 70cm, upgrading coax from RG-58 to LMR-400 is equivalent to multiplying transmit power by 5×.
Does coax loss affect receiving as well as transmitting?

Yes, equally. Feed line loss is reciprocal — if you lose 3 dB transmitting, you also lose 3 dB receiving. This means a noisy, lossy feed line hurts your ability to hear weak signals just as much as it reduces your effective radiated power. Low-noise preamplifiers mounted at the antenna (rather than in the shack) are used on long feed line runs specifically to amplify the signal before the coax loss degrades it on receive.