Fiber Optic Loss Calculator
Fiber optic link loss determines whether a transmitter-receiver pair can communicate reliably over a given distance. Total link loss (dB) = fiber attenuation (dB/km) x length (km) + connectors x loss/connector + splices x loss/splice. A link is viable when total loss is less than the optical power budget minus the safety margin. This calculator adds all loss components and compares them to the power budget. Typical single-mode fiber at 1550 nm has 0.20 dB/km attenuation per ITU-T G.652D. Each connector pair typically adds 0.5 dB, and each fusion splice adds about 0.1 dB.
Fiber optic loss formula
Total loss (dB) = alpha x L + Nc x Lc + Ns x Ls
Margin (dB) = Power budget - Total loss
Where alpha = attenuation in dB/km, L = length in km, Nc = connector pairs, Lc = loss per connector pair, Ns = splices, Ls = loss per splice. Positive margin = link is viable.
Fiber attenuation reference values
- ITU-T G.652D single-mode, 1310 nm: maximum 0.35 dB/km (typical 0.30 dB/km).
- ITU-T G.652D single-mode, 1550 nm: maximum 0.20 dB/km (typical 0.18 dB/km).
- OM3 multimode (50/125 um), 850 nm: 3.0 dB/km maximum per TIA-568.
- OM4 multimode (50/125 um), 850 nm: 3.5 dB/km maximum but typically 2.5 dB/km.
Fiber optic loss: frequently asked questions
How is fiber optic loss measured?
Fiber optic loss is measured in decibels (dB). Total link loss = fiber attenuation (dB/km) x length (km) + number of connectors x loss per connector (dB) + number of splices x loss per splice (dB). The result is compared against the system power budget (transmitter output minus receiver sensitivity) to determine if the link will work.
What is typical fiber attenuation?
Single-mode fiber (SMF-28) at 1310 nm: approximately 0.35 dB/km. At 1550 nm: approximately 0.20 dB/km. Multimode OM3/OM4 at 850 nm: 2.0 to 3.5 dB/km. Plastic optical fiber (POF) is much higher, around 0.15 to 0.20 dB/m. ITU-T G.652 specifies attenuation for standard single-mode fiber.
How much loss does a connector add?
A typical LC, SC, or FC connector pair (two mated connectors) adds 0.3 to 0.5 dB. High-quality factory-terminated connectors can be as low as 0.1 dB. Field-polished connectors may add 0.5 to 1.0 dB. Fusion splices add 0.02 to 0.05 dB; mechanical splices add 0.1 to 0.5 dB.
What is the power budget?
The power budget is the maximum allowable loss between transmitter and receiver: power budget = transmitter output power (dBm) - receiver sensitivity (dBm). For a link to work, total link loss must be less than the power budget minus any safety margin (typically 3 dB).
What is the difference between single-mode and multimode fiber?
Single-mode fiber (9/125 um core/cladding) carries one spatial mode and has lower attenuation and higher bandwidth, suitable for long distances (km to hundreds of km). Multimode fiber (50/125 or 62.5/125 um) supports many modes and is used for shorter distances (up to about 2 km for OM5) at lower cost with LED or VCSEL sources.
Official sources
- ITU-T G.652: Characteristics of a single-mode optical fibre and cable. itu.int.
- TIA-568.3-D: Optical Fiber Cabling Components Standard. tiaonline.org.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.