Fiber Utilization Calculator
Measure how much of a fiber plant is lit: strands in use, wavelengths per pair, spare capacity and dark-fiber headroom.
Inputs
Strand Utilisation
25.0%
Wavelength Utilisation on Lit Pairs
30.0%
Capacity in Service
14.40Tbps
Total Potential Capacity
192.00Tbps
Dark Strands Remaining
72
Step by step
Values used
Fiber strands in the cable = 96 strands; Strands currently lit = 24 strands; DWDM channels per fiber pair = 40 channels; Channels in service per lit pair = 12 channels; Capacity per channel = 100 Gbps
Fiber Utilization
strand utilisation = lit strands ÷ total strands; capacity = lit pairs × channels in service × per-channel rate.
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
How it works
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
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.
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