Estimate passive optical attenuation from fiber type, wavelength, distance, connectors, splices, bend events, and reserve margin for home lab and small site fiber runs. Fiber attenuation rate (dB/km) Use measured cable loss here if your reel, OTDR trace, or datasheet is more specific. It's measured in decibels per kilometer (dB/km), and it determines how far a signal can travel before it becomes too weak to read. A standard single-mode fiber operating at 1550 nm loses. This calculator helps you estimate the total attenuation (signal loss) in a fiber optic cable link. distance with real-time graphing.