Fibre optic link-loss budget calculator
Calculate optical loss on a fibre link and check it against your SFP's power budget.
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Choose the fibre type, enter the length, number of connectors and splices, and add a safety margin. The calculator gives the total link loss. Enter the transmitter power and receiver sensitivity of your SFPs to see whether the link will work and the receive power you should expect.
Typical loss values
- Single-mode fibre: 0.35–0.4 dB/km at 1310 nm, 0.25–0.3 dB/km at 1550 nm
- Multimode OM3/OM4: about 3 dB/km at 850 nm
- Mated connector pair: 0.3–0.75 dB
- Fusion splice: 0.05–0.1 dB
Power budget
The power budget is the transmitter's minimum output power minus the receiver's sensitivity, both in dBm. The link works if the total loss, including a safety margin of 3 dB for ageing and repairs, is less than the power budget. Also check the receiver's overload limit on short links with long-reach optics; you may need an attenuator.
Test after installation
Calculations predict the loss; an OTDR trace and a light-source power-meter test prove it. We test and document every link we install.
Common questions
How much loss is acceptable on a fibre link?
Any loss that leaves at least 3 dB of margin within your optics' power budget. For example, 1000BASE-LX optics with an 11 dB budget can typically run 10 km of single-mode fibre with a few connectors.
What is the difference between single-mode and multimode?
Single-mode has a small core and runs for kilometres. Multimode has a larger core and is used inside buildings, typically up to 300–550 m at 10 Gbps on OM3/OM4.
Why do I need a safety margin?
Fibre gets repaired, connectors get dirty and components age. A 3 dB margin keeps the link working through all of these.
