Fiber Utilization Calculator

Measure how much of a fiber plant is lit: strands in use, wavelengths per pair, spare capacity and dark-fiber headroom.

About Fiber Utilization Calculator

Fiber has two independent dimensions of headroom: unlit strands and unused wavelengths on the strands already lit. Adding channels to an existing pair is a transponder purchase, while lighting new strands is a much larger optical-line-system project. Knowing which kind of headroom you have decides whether the next 400G service is a card order or a capital project — and whether the route needs new fiber at all.

Formula

Fiber Utilization

strand utilisation = lit strands ÷ total strands; capacity = lit pairs × channels in service × per-channel rate.

lit pairs: Lit strands ÷ 2, since transmission needs one strand each way
per-channel rate: Line rate of a single DWDM wavelength

Worked example

With the default values below, Fiber Utilization Calculator returns Strand Utilisation of 25.0%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Fiber strands in the cableaccepts 2–3,456 strands: 96 strands
Strands currently litaccepts 0–3,456 strands: 24 strands
DWDM channels per fiber pairaccepts 1–192 channels: 40 channels
Channels in service per lit pairaccepts 0–192 channels: 12 channels
Capacity per channelaccepts 1–1,600 Gbps: 100 Gbps

Results

Strand Utilisation: 25.0%
Wavelength Utilisation on Lit Pairs: 30.0%
Capacity in Service: 14.40 Tbps
Total Potential Capacity: 192.00 Tbps
Dark Strands Remaining: 72

Step by step

1Values used
2Fiber Utilization
3Strand Utilisation= 25.0
4Wavelength Utilisation on Lit Pairs= 30.0
5Capacity in Service= 14.40 Tbps
6Total Potential Capacity= 192.00 Tbps
7Dark Strands Remaining= 72

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Fiber Utilization calculated?

strand utilisation = lit strands ÷ total strands; capacity = lit pairs × channels in service × per-channel rate. Fiber has two independent dimensions of headroom: unlit strands and unused wavelengths on the strands already lit. Adding channels to an existing pair is a transponder purchase, while lighting new strands is a much larger optical-line-system project.

Why does Fiber Utilization matter?

Knowing which kind of headroom you have decides whether the next 400G service is a card order or a capital project — and whether the route needs new fiber at all.

What values do I need to enter?

This calculator takes 5 inputs: Fiber strands in the cable, Strands currently lit, DWDM channels per fiber pair, Channels in service per lit pair, Capacity per channel. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.