Cable Loss Budget

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Equation / Last modified by KurtHeckman on 2019/03/01 01:46
KurtHeckman.Cable Loss Budget

The Fiber-optic Cable dB Loss Budget calculator computes the transmission loss budget (allowance) in dB over a distance of fiber optic cable based on the length of the cable (L), type of cable (FT), number of connectors (C), the dB loss per connector (CL), the number of splices (S), and the dB loss per connector (CL). 

INSTRUCTIONS:  Choose your preferred units and enter the following:

  • (C) This is the number of mated connector pairs.
  • (CL) This is the dB loss per mated connector pair (0.75 dB default).
  • (S) This is the number of splices.
  • (SL) This is the dB loss per splice (0.3 dB default).
  • (FT) Choose a type of fiber-optic cable (see list below).
  • (L) This is the total length of the cable.

dB Loss Budget: The calculator returns the transmission Loss Budget in dB.  The Loss Budget is a reasonable expected transmission loss (attenuation) based on normal factors.  If the loss is greater than the budget, one must assume that loss in the system is due to abnormal circumstances that need to be corrected.

The Math / Science


To test a fiber optic cable plant, you need to perform a loss test.   The loss across a fiber-optic line is a function of the loss in the fiber optic cable itself and the loss introduced by connectors and splices. 

The typical mated connector pair loses 0.75 dB for each connector.    A splice typically introduces 0.3 dB loss. 

The loss for different types of fiber cable is as follows:

  • 1550 nm singlemode fiber loses 0.4 dB every kilometer.
  • 1310 nm singlemode fiber loses 0.5 dB every kilometer.
  • 1300 nm multimode fiber loses 1.0 dB every kilometer.
  • 850 nm multimode fiber loses 3.0 dB every kilometer.

If the transmission loss rate is different than the options above, used the dB Loss Calculator.  The dB Loss Calculator lets you manually enter the dB loss per kilometer.

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This calculator is dedicated to all of the fiber-optic techs and engineers who worked on Groundbreaker and Axis, especially the Sycamore crew.

  • Hall of Fame:  LaRue, Ken, Hal, Wayne, Bill, Alton, Jamie, Wade, John, Fred, Lance, David, Cody