Fiber DB loss calculator — Free Online CalculatorTurn distance into loss—or loss into distance.

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Fiber DB Loss Calculator, with a useful next step.

A fiber DB loss calculator estimates the attenuation contributed by the glass path itself. The core relationship is simple: fiber distance in kilometers multiplied by the attenuation coefficient in dB/km equals the expected fiber loss in dB. The coefficient depends on fiber family, operating wavelength, cable construction, and the exact product datasheet. This tool therefore shows the wavelength choices for the selected product instead of presenting one universal number. It includes common single-mode references such as OS2 G.652D, G.655, and G.657, plus multimode families from OM1 through OM5. Use Distance → loss when planning a cable run, checking a measured span, or estimating the fiber portion of a link budget. Use Loss → distance when a receiver or system budget gives you a maximum fiber-only allowance. The result intentionally excludes connector pairs, fusion splices, splitters, transceiver tolerances, and engineering margin; those items belong in a complete link loss budget. If the required wavelength is not listed, choose Custom and enter the coefficient from the exact cable datasheet. The linked low-loss fiber article provides additional context before the result is used for purchasing or acceptance testing.