Fiber optic loss budget calculator

It is the accounting of how much optical power a link loses end to end, compared to how much the equipment can afford to lose. You add up the loss from the cable itself, every connector, and every splice, then compare that total to the power budget of the transceivers. If the loss is less than the budget, the link works; the difference is your margin.

Multiply the length in kilometers by the fiber's attenuation in dB per km, add the number of connectors times the per-connector loss, and add the number of splices times the per-splice loss. Total loss equals cable plus connectors plus splices. The calculator above does this and checks it against your budget.

TIA-568 allows up to 0.75 dB per mated connector pair, though clean, well-seated connectors are often nearer 0.3 dB. A fusion splice is typically about 0.1 dB and is allowed up to 0.3; a mechanical splice runs closer to 0.3. The calculator defaults to 0.5 dB per connector and 0.1 dB per fusion splice, both editable.

Single-mode OS2 loses roughly 0.35 dB per km at 1310 nm and about 0.22 dB per km at 1550 nm, which is why long outside-plant runs use it. Multimode OM3/OM4 loses about 3.0 dB per km at 850 nm and around 1.5 dB per km at 1300 nm, fine for short in-building runs but far lossier over distance.

Keep some headroom rather than running to zero. A common target is about 3 dB of margin above the calculated loss to cover fiber aging, a connector that gets dirty, and the occasional repair splice added later. A link that only just closes today can drift out of budget over its life.

The power budget is the transmit power minus the receiver sensitivity, both read off the optics datasheet in dBm. For example a transmitter at -3 dBm into a receiver good to -20 dBm gives a 17 dB budget. Enter it directly, or use the Tx and Rx fields in the calculator to work it out.