Fiber Loss Budget Calculator
Optical loss budget from TIA-568.3-D component allowances — fiber, connectors, splices, with margin guidance.
| Fiber attenuation (0.366 km) | 0.18 dB |
| Connector pairs (2 × 0.75) | 1.50 dB |
| Splices (1 × 0.30) | 0.30 dB |
| Calculated loss budget | 1.98 dB |
Installed links should test comfortably under 1.98 dB — a result near the budget on a new link is a workmanship flag.
Where the math comes from.
How the calculation works
A loss budget is the sum of named contributions: fiber attenuation (length × dB/km for the fiber type and wavelength), plus an allowance for every mated connector pair, plus an allowance for every splice. This tool uses the ANSI/TIA-568.3-D maximum component values by default — 0.75 dB per mated connector pair and 0.3 dB per splice — with cable attenuation maxima per fiber type. Field-measured components routinely beat these numbers; designing to the maxima is what makes the budget defensible at closeout.
Reading the result
The calculated budget is a ceiling, not a target. A healthy installed link should test comfortably under it — when a measured result approaches the calculated maximum, that is a signal to investigate (a marginal connector, an unrecorded splice, a bend), not a result to sign off. Compare the budget against your equipment’s power budget (transmitter launch power minus receiver sensitivity) to confirm the optics can carry the link at all.
Where the defaults come from
Cable attenuation defaults: single-mode outside plant 0.5 dB/km, single-mode inside plant 1.0 dB/km, OM3/OM4 multimode 3.5 dB/km at 850 nm and 1.5 dB/km at 1300 nm — the TIA-568.3-D maxima. Your project specification may be tighter; every value in the tool is editable so the budget matches the spec that governs, not our defaults.
Asked about this one.
The calculator sketches it. The design defends it.
When the number has to survive plan review, bidding, and closeout testing — that's RCDD design work, and it's what we do.