What this RF cable loss calculator does
This tool estimates how much signal you lose in a coaxial cable run at a given frequency. It combines cable attenuation with connector losses so you can quickly estimate total insertion loss and output power. The result is useful for Wi-Fi links, cellular/IoT projects, ham radio feeds, SDR setups, test benches, and any RF link budget where every dB matters.
How RF cable loss works
RF attenuation in coax increases mainly with frequency and length. Higher frequency signals travel with more effective resistance and dielectric losses, so a cable that performs fine at VHF can become very lossy at 2.4 GHz or 5.8 GHz. The longer the cable, the more those losses accumulate.
Main factors that affect attenuation
- Cable construction: dielectric quality, shield design, conductor size, and materials.
- Frequency: loss typically rises as frequency rises.
- Length: total loss scales almost linearly with distance.
- Connectors/adapters: each transition adds insertion loss and mismatch risk.
- Installation quality: tight bends, kinks, water ingress, and poor terminations increase loss.
Formulas used in this calculator
The calculator applies a standard engineering approximation:
- Cable loss (dB) = (attenuation in dB per 100 ft) × (length in ft / 100)
- Total loss (dB) = cable loss + (connector count × loss per connector)
- Output power (dBm) = input power (dBm) − total loss (dB)
- Power delivered (%) = 100 × 10(−total loss / 10)
How to use it correctly
1) Pick cable type or custom attenuation
Use a preset cable when available. For manufacturer-specific cable, choose Custom Attenuation and enter the datasheet value at your operating frequency.
2) Enter frequency and length
Frequency is in MHz. Length can be entered in feet or meters. Internally, the tool normalizes units so the math stays consistent.
3) Add connector losses
Real systems include pigtails, bulkhead connectors, adapters, lightning protectors, and couplers. A rough planning value of 0.1 dB per connector is common, but datasheet values are better.
4) Review output power and efficiency
If you enter input power, the calculator estimates output power and the percentage of power that actually reaches the load.
Example use case
Suppose you run 50 ft of LMR-400 at 915 MHz with two connectors at 0.1 dB each and feed 30 dBm (1 W). You should see a modest cable loss plus connector loss. The output dBm tells you what reaches the antenna or instrument input, and the percentage helps visualize how much energy is lost as heat.
Practical design tips
- Keep RF runs short whenever possible.
- Use lower-loss cable at higher frequencies.
- Avoid unnecessary adapters and jumpers.
- Use proper torque and weatherproofing outdoors.
- Validate assumptions with VNA or power meter measurements when performance is critical.
Final note
This calculator is designed for planning and estimation. Actual loss can vary with temperature, cable batch, connector quality, and installation conditions. For production or mission-critical links, always verify with field measurements.