Coaxial Cable Loss Calculator
Calculate RF coaxial cable attenuation, total cable loss, remaining output power, maximum cable length and typical cable comparisons from frequency, cable type, length and transmit power.
RF-010 focuses on feed-line insertion loss. It does not calculate transmission-line phase, quarter-wave transformer matching, Smith chart impedance transformation or free-space path loss.
Engineering tool
Coaxial Cable Loss Calculator
Calculate RF coax cable attenuation, remaining output power, power ratio, maximum cable length and typical cable comparisons.
Result console
- Cable Type
- Manual attenuation
- Frequency
- 433 MHz
- Cable Length
- 10 m
- Cable Length ft
- 32.808399ft
- Attenuation
- 0.2dB/m
- Attenuation per 100 m
- 20dB/100 m
- Total Cable Loss
- 2 dB
- Power Ratio
- 0.63095734
- Power Remaining
- 63.095734%
- Input Power
- Not required
- Output Power
- Not required
- Output Power dBm
- Not required
- Maximum Cable Length
- 10 m
- Formula Used
- Loss = Attenuation × Length
Cable loss is insertion loss in the feed line. It is not free-space path loss and should be entered as part of a link budget.
Manual attenuation values must match the cable datasheet and frequency.
Formula reference
Coaxial Cable Loss Formulas
Cable attenuation is a positive loss value. Absolute RF power is usually handled in dBm, while cable loss is handled in dB.
Loss(dB) = Attenuation × LengthPout(dBm) = Pin(dBm) - Loss(dB)Ratio = 10^(-Loss / 10)Pout = Pin × RatioLength = Allowed Loss / AttenuationVariable definitions
- Loss
- total cable insertion loss in dB
- Attenuation
- cable loss per unit length
- Length
- physical cable length
- Pin
- transmitter or source power entering the cable
- Pout
- remaining power after cable loss
- Ratio
- linear power ratio after cable attenuation
Worked Examples
10 m cable at 0.2 dB/m
Loss = 0.2 dB/m × 10 m = 2 dB.
20 m cable at 0.15 dB/m
Loss = 0.15 dB/m × 20 m = 3 dB.
100 W with 3 dB loss
Power ratio = 10^(-3/10) = 0.501, so remaining power is about 50 W.
30 dBm with 6 dB loss
Pout = 30 dBm - 6 dB = 24 dBm.
Allowed loss 5 dB, attenuation 0.2 dB/m
Maximum length = 5 dB / 0.2 dB/m = 25 m.
RG58 vs LMR240
At the same length and frequency, LMR240 usually leaves more output power because its attenuation is lower than RG58.
LMR400 vs RG213
LMR400 usually has lower loss than RG213 at UHF and microwave frequencies for antenna feed lines.
5.8 GHz high-frequency feed
Small coaxial cables can lose many dB over short lengths at 5.8 GHz, so cable choice and connector quality become critical.
6 dB receive-side loss
A 6 dB cable loss before a receiver reduces received signal power to about 25%, which can reduce link margin or sensitivity performance.
10 dB feed-line loss
A 10 dB loss means only about 10% of transmitter power reaches the antenna before mismatch and antenna effects.
Engineering Notes
- Coaxial cable loss increases with cable length.
- Cable loss usually increases as frequency rises.
- 3 dB loss leaves about half of the input power.
- 6 dB loss leaves about one quarter of the input power.
- 10 dB loss leaves about one tenth of the input power.
- Cable loss is not free-space path loss.
- Cable loss belongs inside an RF link budget.
- Connector loss, adapter loss and lightning protector loss may need separate budget terms.
- Shielding, bend radius, installation quality and water ingress can change real cable performance.
- Use manufacturer attenuation tables for production RF designs.
Common Mistakes
- Treating cable loss as free-space path loss.
- Ignoring connector, adapter or lightning protector loss.
- Using a low-frequency attenuation value at microwave frequencies.
- Assuming all coaxial cables have the same loss.
- Using dB per 100 ft as if it were dB per 100 m.
- Ignoring receive-side cable loss before a low-noise receiver.
- Forgetting that 3 dB is roughly half power.
- Assuming typical database values are a substitute for the exact cable datasheet.
Support reference
FAQ
How do I calculate coaxial cable loss?
Multiply the cable attenuation by the cable length after converting both values to matching units. For example, 0.2 dB/m over 10 m gives 2 dB cable loss.
Why does cable loss increase with frequency?
Conductor loss, skin effect and dielectric loss generally increase with frequency, so most coaxial cables have higher attenuation at UHF and microwave frequencies than at HF or VHF.
How much power is left after 3 dB loss?
A 3 dB loss leaves about 50% of the input power. The exact power ratio is 10^(-3/10), or about 0.501.
How much power is left after 6 dB loss?
A 6 dB loss leaves about 25% of the input power. This is why feed-line loss can dominate RF system performance.
Which coaxial cable has lower loss?
Larger low-loss cables such as LMR400, LMR600 or Ecoflex 10 usually have lower loss than small flexible cables such as RG174 or RG58, but exact values depend on frequency and manufacturer data.
How do I choose RF cable?
Choose cable from frequency, allowed loss, power rating, impedance, connector type, bend radius, installation environment and cost. Always verify the selected cable datasheet.
Does connector loss matter?
Yes. Connectors, adapters, lightning protectors and poorly installed terminations can add measurable insertion loss, especially at microwave frequencies.
Can I ignore cable loss?
Cable loss may be small in short low-frequency runs, but it should not be ignored in RF link budgets, antenna feeds, Wi-Fi systems, microwave systems or low-noise receive paths.
How long can my coax cable be?
Maximum length is the allowed loss divided by attenuation per length. If the allowed loss is 5 dB and attenuation is 0.2 dB/m, the maximum length is 25 m.
Is cable loss the same as free-space path loss?
No. Cable loss is insertion loss inside a coaxial feed line. Free-space path loss is propagation loss between antennas and is calculated separately.
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In_DevelopmentDisclaimer
This calculator provides typical RF cable-loss estimates. Final systems should be verified with manufacturer cable data, connector data, measured insertion loss and full link-budget review.