Coax Cable Loss Calculator
Estimate attenuation (dB), power delivered, and received power for common coax cable types.
Tip: 3 dB loss = about half the power. 10 dB loss = about one-tenth the power.
Why a Coax Cable Loss Calculator Matters
Coaxial cable loss directly affects signal quality in RF systems, Wi-Fi backhaul links, cellular boosters, scanner setups, ham radio stations, and CCTV networks. Even with excellent radios and antennas, a poor cable choice can quietly drain performance before the signal reaches the antenna.
A coax cable loss calculator helps you answer practical questions fast:
- Will this cable run be too long at my operating frequency?
- Should I upgrade from RG-58 to LMR-400?
- How much transmit power is actually reaching my antenna?
- Is my weak receive signal partly cable loss?
How Coax Attenuation Works
Coax attenuation is usually expressed in dB per 100 feet (or dB per 100 meters), and it increases as frequency increases. That means cable that performs acceptably at VHF may become very lossy at 2.4 GHz or 5.8 GHz.
Core equation:
Total Cable Loss (dB) = (Cable Length in ft / 100) × Attenuation (dB/100 ft)
Then add: connector loss + any splitter or inline device loss.
Power ratio from dB: Power Out / Power In = 10-Loss/10
What This Calculator Includes
1) Cable type lookup
The calculator contains typical attenuation curves for common cable families:
- RG-58
- RG-59
- RG-6
- RG-8
- LMR-240
- LMR-400
Values are estimated and interpolated across frequency points to provide realistic planning numbers.
2) Length conversion
You can enter length in feet or meters. Internally, the calculator converts to feet for a consistent dB/100 ft calculation.
3) Connector and fixed losses
Real systems include connectors, adapters, lightning protectors, duplexers, and splitters. The calculator lets you add connector count and fixed extra loss so your estimate better matches real-world performance.
4) Power delivery estimate
If you enter transmit power in watts, the tool estimates received watts at the far end of the cable after total loss.
Example Calculation
Suppose you run 50 ft of LMR-400 at 2.4 GHz with two connectors and no extra fixed loss:
- Typical cable attenuation might be around 4.6 dB/100 ft.
- Cable-only loss: 50/100 × 4.6 = 2.3 dB.
- Connector loss: 2 × 0.05 = 0.1 dB.
- Total estimated loss: 2.4 dB.
A 2.4 dB loss means roughly 57.5% of power reaches the load. If you launched 10 W, you'd receive about 5.75 W at the far end of the cable.
Choosing the Right Coax for Your Frequency
Low frequencies (HF/VHF)
Longer runs can be acceptable with mid-grade cable. Loss is lower, so budget constraints often drive cable choice.
UHF and above
Loss rises quickly. Shorter runs and better coax (larger diameter, lower-loss dielectric) become much more important.
2.4 GHz and 5.8 GHz links
At microwave frequencies, cable loss can be severe. Keep runs short, avoid unnecessary adapters, and use high-performance coax if cable cannot be avoided.
Practical Tips to Reduce Coax Loss
- Shorten cable runs: every foot counts at higher frequencies.
- Use better cable: low-loss cable often pays for itself in performance.
- Minimize adapters: each junction can add insertion loss and mismatch.
- Check connectors: poor terminations can add hidden losses and reflections.
- Validate with instruments: for critical systems, verify with a VNA, cable analyzer, or field meter.
Frequently Asked Questions
Is this calculator accurate enough for engineering work?
It's excellent for planning and comparison. For final design, always confirm with manufacturer datasheets for your exact cable part number and operating temperature.
Why does frequency matter so much?
Higher-frequency current crowds toward conductor surfaces (skin effect), and dielectric losses also increase, both of which raise attenuation.
What does a 3 dB cable loss mean?
About half your power is lost in the cable. For receive paths, that also means weaker signal levels reaching your radio.
Bottom Line
A coax cable loss calculator helps you make smarter RF decisions before you buy hardware or install a long feedline. Use it to compare cable types, estimate real delivered power, and avoid costly performance surprises.
Note: attenuation values are representative estimates. Always verify final values from official cable datasheets for critical deployments.