Fiber Optic Loss & Link Budget Calculator
Estimate fiber link loss from length, connectors and splices (TIA maximums or your own values), then check received power and margin against the receiver, in dBm and mW.
TIA-568 maximums are planning values: 0.75 dB per mated connection, 0.3 dB per splice, and the cable attenuation of the chosen fiber. Real links usually measure better — test the installed link.
| dBm | mW |
|---|---|
| 10 | 10 |
| 5 | 3.162 |
| 3 | 1.995 |
| 0 | 1 |
| -3 | 0.5012 |
| -7 | 0.1995 |
| -10 | 0.1 |
| -15 | 0.03162 |
| -20 | 0.01 |
| -30 | 0.001 |
A fiber link works when the light that reaches the receiver is above its sensitivity, with some margin left over. This calculator adds the losses along the way (fiber attenuation per kilometre, every mated connector pair, every splice and any splitter) and compares them with the transmitter power and receiver sensitivity. Use TIA-568 maximums for a safe design, or your own datasheet values. A second mode turns two power-meter readings into a measured loss.
How to use this tool
- Pick the fiber type and wavelength, or enter the attenuation from the cable datasheet.
- Enter the length, the number of mated connector pairs and splices, and any splitter loss.
- Enter the transceiver's transmitter power and receiver sensitivity, plus the safety margin you want.
- Read the total loss, received power and margin — or switch to measured mode and enter your meter readings.
Formula
loss = attenuation × length + connections × loss each + splices × loss each + other; margin = (Tx − sensitivity) − loss; mW = 10^(dBm ÷ 10)
Decibels add along the link, which is why losses are summed. Received power in dBm = transmitter dBm − loss. Every 3 dB halves the power and every 10 dB divides it by ten. The TIA maximums used for the presets are 0.75 dB per mated connection, 0.3 dB per splice, 3.0 or 3.5 dB/km for multimode at 850 nm, 1.5 dB/km at 1300 nm, and 1.0 (inside plant) or 0.5 dB/km (outside plant) for single-mode.
Example
A 10 km single-mode link at 0.35 dB/km loses 3.5 dB in the fiber, 1.5 dB in two connections and 0.6 dB in two splices: 5.6 dB in total. With a −3 dBm transmitter and a −20 dBm receiver the budget is 17 dB, so the light arrives at −8.6 dBm (about 0.14 mW) and the margin is 11.4 dB — 8.4 dB more than a 3 dB safety margin.
Frequently asked questions
How much margin should a link have?
Designers commonly keep 3 dB or more for ageing, extra repair splices and dirty connectors. A link that only passes with zero margin will fail as soon as one connector gets contaminated.
Why does my measured loss differ from the calculation?
With TIA maximums the calculation is a worst case, so good installations measure lower. Loss above the calculation points to a dirty or damaged connector, a tight bend or a bad splice: clean the connectors first, then check with an OTDR.
Can there be too much light?
Yes. Long-reach optics on a short link can push the received power above the receiver's overload level and cause errors. Enter the overload figure from the datasheet; the calculator tells you how big an attenuator to add.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/fiber-loss-tool/
Cite or embed this tool
kakaoCalc. (2026, November 8). Fiber Optic Loss & Link Budget Calculator. https://kakao.mobile/tools/fiber-loss-tool/
“Fiber Optic Loss & Link Budget Calculator.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/fiber-loss-tool/.
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