Tool

Fiber Link Loss Budget Calculatorend-to-end dB math for PON, Ethernet, and DWDM links.

Enter your link details step by step. The calculator runs all the math instantly in your browser — fiber attenuation over distance, connector pairs, splices, splitter and bypass losses, transmitter output, receiver sensitivity, power penalty, and your repair margin — and shows the System Performance Margin in dB.

Step 1

Cable distance and fiber loss per km

Length of the fiber run, plus per-km attenuation at your operating wavelength.

Cable distance

Unit

Loss per km

Custom loss per km (dB/km) — select Other to edit

Step 2

Connector pairs

Loss per mated connector pair × number of pairs. Do not count equipment-end connectors.

Loss per connector pair (dB)

TIA-568 recommended maximum: 0.75 dB

Number of connector pairs

Step 3

Splices (fusion or mechanical)

Per-splice loss × number of splices in the link.

Loss per splice (dB)

TIA-568 recommended maximum: 0.30 dB

Number of splices

Step 4

Other in-line losses

Bypass switches, optical splitters, and any other passive component in the path.

Optical bypass switch (dB)

Optical splitter (dB)

Use the datasheet IL; e.g. 10.8 dB for a 1×8 PLC

Other components (dB)

Passive concentrators, WDM couplers, etc.

Step 5

System gain

Transmitter average output power minus receiver minimum sensitivity.

Avg. transmitter output (dBm)

Min. receiver sensitivity (dBm)

Step 6

Power penalty and repair margin

Additional allowance for dispersion, reflections, and future field repairs.

Power penalty (dB)

Dispersion, reflection, aging

Repair margin (dB)

Allowance for future splices / cable swaps

How the link loss budget is computed

A fiber link works if the total attenuation between transmitter and receiver is less than the system gain (transmitter output minus receiver sensitivity), after subtracting a power penalty and a field-repair margin. The calculator walks through the seven standard components:

Total fiber loss = cable distance in km × loss per km. The calculator accepts feet, miles, meters, or kilometers and converts internally using exact constants (1 ft = 0.0003048 km; 1 mi = 1.609344 km).
Total connector loss = loss per connector pair × number of pairs. TIA-568 recommends a maximum of 0.75 dB per pair.
Total splice loss = individual splice loss × number of splices. TIA-568 recommends a maximum of 0.30 dB per splice for fusion work.
Other component loss = optical bypass switch + splitter + any other in-line passive device.
System gain = average transmitter output (dBm) − minimum receiver sensitivity (dBm).
Total power penalty + margin = power penalty (dispersion, reflections) + repair margin (allowance for future splices or cable replacement).
System performance margin = total link loss budget − total cable system attenuation. Positive = you have headroom; negative = the link will not close and you need to shorten the run, change fiber type, or pick a transceiver with more gain.

Just need the splitter loss? For a quick 10·log₁₀(N) split-loss estimate without a full link model, use the Optical Splitter Loss Calculator.

Loss-per-km presets explained

The Step 1 wavelength preset matches typical fiber datasheet values:

Wavelength	Preset (dB/km)	Typical fiber
850 nm	3.50 / 3.75	OM1/OM2/OM3/OM4 multimode
1300 nm	1.00 / 1.50	OM1/OM2 multimode
1310 nm	0.35 / 0.40 / 0.50	Single-mode G.652D/G.657A
1550 nm	0.25 / 0.40 / 0.50	Single-mode G.652D/G.657A
Other	custom	Enter a vendor-specific value