Coax Cable Loss Calculator
Estimate insertion loss (dB) based on cable type, frequency, run length, temperature, and connector losses.
What this calculator helps you estimate
Coaxial cable attenuation is the power loss that occurs as RF energy travels through a cable run. This tool helps you quickly estimate that loss in decibels (dB), including both cable loss and connector loss. It is useful for radio systems, Wi-Fi backhaul links, scanner installations, TV systems, telemetry nodes, and lab test setups.
Because attenuation increases with frequency and run length, two systems with identical hardware can perform very differently if their coax choices are different. A clean estimate lets you decide whether to shorten the run, upgrade cable type, or move active equipment closer to the antenna.
How coax attenuation is modeled
1) Frequency-dependent cable loss
Most real-world coax loss curves can be approximated with a two-term model:
Loss (dB/100m) = A × √f + B × f
- f is frequency in MHz
- A captures conductor/skin-effect-dominant behavior
- B captures dielectric and high-frequency slope
The calculator includes practical coefficients for common cable families and lets you enter custom values from manufacturer datasheets.
2) Length scaling
Once dB per 100 meters is estimated, total cable-only loss scales linearly with length:
Cable loss (dB) = Loss(dB/100m) × (length_m / 100)
3) Temperature effect
Attenuation usually rises with temperature. This calculator applies a simplified +0.2% per °C adjustment relative to 20°C. It is a reasonable planning assumption for many PE-foam coax products, though datasheet values should be used for final engineering.
4) Connector loss
Each connector adds insertion loss. The total is:
Total loss = Cable loss + (connector count × connector dB each)
Interpreting the results
- Total attenuation (dB): end-to-end link loss in the coax path.
- Power ratio: fraction of power delivered after cable and connectors.
- Estimated output power: shown if you enter input power in watts.
Quick intuition: every 3 dB is about half power, 6 dB is about one-quarter, and 10 dB is one-tenth.
Example planning scenario
Suppose you are running 30 meters of LMR-400 at 915 MHz with two connectors at 0.15 dB each. The calculator will show a practical estimate of total path attenuation and how much transmitter power is left at the far end. If the loss is too high for your link margin, your best improvements are usually:
- Use lower-loss coax (larger diameter cable generally helps),
- Shorten the cable run,
- Reduce connector count or improve connector quality,
- Move radio equipment closer to the antenna and run longer low-frequency lines instead.
Choosing the right cable type
When low cost matters most
RG-58 and RG-6 are common and affordable, but they attenuate significantly at higher frequencies and longer runs.
When RF performance matters most
LMR-400 or corrugated hardline (like 1/2" Heliax class cable) generally provide much lower attenuation, especially above a few hundred MHz.
Impedance check
Use 50Ω cable for most RF communications equipment and 75Ω cable for many video/cable-TV systems. Mismatched impedance can introduce reflections and additional losses not captured by this simple attenuation model.
Practical tips to reduce attenuation in real installations
- Keep runs as short and direct as possible.
- Avoid tight bends that exceed cable bend-radius limits.
- Use weatherproofing on outdoor connectors to prevent moisture ingress.
- Choose high-quality connectors and correct crimp/solder tooling.
- Verify link performance with a VNA, cable analyzer, or power meter when possible.
Limitations and assumptions
This calculator is meant for engineering estimates and educational planning. Real attenuation depends on exact cable construction, frequency band, manufacturing tolerance, aging, moisture exposure, and installation quality. For mission-critical work, always confirm with manufacturer attenuation tables and field measurements.