Coax Loss Calculator
Find total signal attenuation in dB and the remaining power fraction for a coax cable run. Requires the attenuation factor from the manufacturer's spec sheet.
From the cable manufacturer's spec sheet at the operating frequency.
Result
6.1 dB
100 ft of cable at 6.1 dB/100ft loses 6.1 dB, leaving about 24.5% of the signal power
Quick Answer
A coax loss calculator multiplies cable length by the manufacturer's rated attenuation factor (in dB per 100 ft) and divides by 100 to get total cable loss in dB. For a 250 ft run of cable rated at 6.5 dB per 100 ft, attenuation = 250 ÷ 100 × 6.5 = 16.25 dB. The remaining power fraction is 10^(−16.25 ÷ 10) = 0.0237, meaning about 2.4% of transmitted power reaches the far end.
How a Coax Loss Calculator Uses the Spec Sheet Value
A coax loss calculator requires one input that is not generic: the attenuation factor in dB per 100 ft (or dB per 100 m) for your specific cable type at your operating frequency. This value must come from the manufacturer's data sheet for the exact cable you are using. It is not a universal constant and it cannot be estimated from the cable's physical appearance or connector type alone. Attenuation increases with frequency, so a cable that loses 4 dB per 100 ft at 100 MHz may lose 9 dB per 100 ft at 1 GHz.
The Coax Loss Formula: Attenuation and Power Fraction
Attenuation (dB) = cable length (ft) ÷ 100 × attenuation factor (dB per 100 ft) Power fraction remaining = 10^(−attenuation dB ÷ 10)
- Attenuation (dB) = cable length (ft) ÷ 100 × attenuation factor (dB per 100 ft)
- Power fraction remaining = 10^(−attenuation dB ÷ 10)
Use the Coax Loss Calculator With These Inputs and Steps
Inputs
- Cable length (ft): measure the actual installed cable run length, including any slack or routing around obstructions
- Attenuation factor (dB per 100 ft): from the cable manufacturer's specification table at the operating frequency of your system
Steps
- Measure or obtain the cable run length in feet.
- Look up the attenuation factor in the cable manufacturer's spec sheet at your operating frequency.
- Enter both values into the calculator.
- Read total attenuation in dB and the remaining power fraction.
- Compare total attenuation to the system link budget to confirm the link is viable.
Coax Loss Worked Example: 300 ft Run at Two Frequencies
A 300 ft coax run evaluated at 100 MHz (2.0 dB/100 ft) and 1 GHz (7.5 dB/100 ft).
- At 100 MHz: 300 ÷ 100 × 2.0 = 6.0 dB attenuation.
- Power fraction at 100 MHz: 10^(−6.0 ÷ 10) = 0.251 (25.1% power remaining).
- At 1 GHz: 300 ÷ 100 × 7.5 = 22.5 dB attenuation.
- Power fraction at 1 GHz: 10^(−22.5 ÷ 10) = 0.0056 (0.56% power remaining).
Loss increases from 6.0 dB (25.1% power) at 100 MHz to 22.5 dB (0.56% power) at 1 GHz.
When the Coax Loss Calculator Guides a Link Budget
Use this calculator during system design to check whether a planned cable run creates too much signal loss for the receiver to decode the signal. It is also useful for diagnosing an existing installation where signal level is low, by quantifying the expected cable contribution to the loss budget. For satellite, antenna, and RF distribution systems, compare total cable loss to the available link margin. If total cable attenuation approaches or exceeds the link margin, consider a shorter run, a lower-loss cable grade, or an inline amplifier at the appropriate point in the signal path.
Assumptions
- The attenuation factor is constant over the cable length (no splice or connector losses are included).
- The attenuation factor is taken from the manufacturer's spec sheet at the actual operating frequency; the calculator does not interpolate between frequency points.
- Cable length is the full physical run including any bends and slack; a straight-line distance understates the actual cable length.
Limitations
- Does not include connector losses; each connector or splice typically adds 0.1 to 0.5 dB depending on type and quality.
- Does not interpolate attenuation factors across frequencies; look up the correct value for your operating frequency directly from the spec sheet.
- Does not account for temperature effects on attenuation; loss increases slightly at higher temperatures and with cable aging.
- Does not calculate cable length given a loss budget; rearrange the formula manually: length = (target dB ÷ attenuation factor) × 100.
In Practice
The most common coax loss error is using an attenuation factor from a generic cable chart rather than from the specific cable's data sheet at the operating frequency. Generic charts list nominal values that can differ from the actual cable by 20 to 30%. For a broadcast, antenna, or satellite application where the link margin is tight, this difference matters. Download the spec sheet for the exact cable part number and use the attenuation table at the frequency column closest to your operating frequency.
Related Calculators
Related Guides
- How To Calculate Coax Cable Loss
Learn how to calculate coax cable signal loss (attenuation). Find out exactly how frequency, cable type, and length drain your RF signal strength.
- How To Calculate Solar Battery Storage Needs
Learn how to calculate solar battery storage needs based on daily kWh, days of autonomy, and battery limits. See the formula and a full worked example.
- How To Calculate Sprocket Ratio
Learn how to accurately calculate sprocket ratio to determine the output speed of a chain drive. Walk through the teeth and RPM formulas step by step.
- How To Calculate Torque Conversion
Learn how to calculate torque conversions between Newton-meters, foot-pounds, and inch-pounds. Understand the exact mathematical conversion factors.
- How to Calculate True Position in GD&T: Full Guide
Understand true position in GD&T: the formula, how the diametric tolerance zone works, and a complete step-by-step example using X and Y coordinate deviations.
- How To Calculate Volumetric Flow Rate Step By Step
Learn how to calculate volumetric flow rate from area and velocity, convert pipe diameter to area, and reverse the formula for pipeline velocity.
Frequently Asked Questions: Coax Loss Calculator
What is attenuation in a coaxial cable?
Attenuation is the reduction in signal power as the signal travels along the cable, expressed in decibels (dB). It results from resistive losses in the center conductor and shield and from dielectric losses in the insulating layer between them. Attenuation increases with frequency and cable length.
Where do I find the attenuation factor for my cable?
The attenuation factor (dB per 100 ft) appears in the manufacturer's specification sheet or datasheet for the exact cable model you are using. It is typically listed in a table with multiple frequency columns, often covering 50 MHz to several GHz. Use the value at the column closest to your operating frequency.
What does 3 dB of cable loss mean?
A 3 dB loss means half the transmitted power reaches the far end of the cable. A 6 dB loss means one-quarter of the power remains. A 10 dB loss means one-tenth of the power remains. Each additional 3 dB of loss halves the remaining power again.
Can I use one attenuation factor for all frequencies?
No. Attenuation is strongly frequency-dependent. A coax cable rated at 2 dB per 100 ft at 100 MHz may have 8 or more dB per 100 ft at 1 GHz. Always use the factor from the spec sheet at the specific operating frequency of your system, not a generic or DC resistance-based estimate.
How do I account for connector losses in the total cable loss?
Add connector insertion loss separately. Each connector or splice typically adds 0.1 to 0.5 dB depending on type, frequency, and quality of installation. For a run with connectors at each end, add 0.2 to 1.0 dB to the total cable attenuation calculated by this tool.
Sources
Last updated: . Reviewed for accuracy against the formula shown above.