WDM Channel Spacing Calculator
Calculate wavelength division multiplexing channel count, spacing, and aggregate bandwidth for CWDM and DWDM systems.
About this calculator
Wavelength division multiplexing (WDM) carries multiple independent signals over a single fiber by assigning each one its own wavelength ("channel"), packed as tightly as the equipment's channel spacing allows. This calculator looks up the channel spacing and maximum channel count for the WDM Type you select, following the ITU-T standardized spectral grids -- CWDM (ITU-T G.694.2) spaces channels 20nm apart for up to 18 channels, while DWDM (ITU-T G.694.1) packs channels much more tightly (0.8nm/100GHz, 0.4nm/50GHz, or 0.2nm/25GHz depending on the grid) for up to 44, 88, or 160 channels respectively, at correspondingly higher equipment cost and MUX/DEMUX insertion loss. Usable Channels is capped at the WDM Type's maximum, so once Channels Needed reaches that cap, adding more requested channels stops increasing Total Bandwidth entirely -- the calculator flags this with Channels Fit rather than silently under-delivering.
Total Bandwidth itself is a straightforward product of Usable Channels, Data Rate per Channel, and Fiber Pairs, so any one of those three inputs scales the aggregate capacity proportionally. This is a planning-level estimate: real-world DWDM systems also depend on amplifier spacing, chromatic dispersion, and transceiver reach, none of which are modeled here.
Inputs
Results
Usable Channels
8
Total Bandwidth
80 Gbps
Figures current as of 2020. Sources: ITU-T Recommendation G.694.2, "Spectral grids for WDM applications: CWDM wavelength grid", International Telecommunication Union Telecommunication Standardization Sector — defines the 18-wavelength, 20nm-spaced CWDM grid this calculator's CWDM option is built on, ITU-T Recommendation G.694.1, "Spectral grids for WDM applications: DWDM frequency grid", International Telecommunication Union Telecommunication Standardization Sector — defines the 100 GHz (0.8nm), 50 GHz (0.4nm), and 25 GHz (0.2nm) DWDM channel grids this calculator's DWDM options are built on
How to Use This Calculator
- Select WDM Type: CWDM (20nm spacing, up to 18 channels) or DWDM at 100GHz, 50GHz, or 25GHz spacing (up to 44, 88, or 160 channels respectively).
- Enter Channels Needed and Data Rate per Channel (Gbps) for your capacity requirement.
- Set Fiber Pairs available in your cable plant.
- Review Usable Channels, Total Bandwidth (Gbps), Channel Spacing (nm and GHz), and Spectrum Used.
- Check Channels Fit (1=Yes) and MUX + DEMUX Loss (dB) — add this to your optical power budget calculation.
How the result changes with Channels Needed
| Channels Needed | Usable Channels | Total Bandwidth |
|---|---|---|
| 4 | 4 | 40 Gbps |
| 6 | 6 | 60 Gbps |
| 12 | 12 | 120 Gbps |
| 20 | 20 | 200 Gbps |
What each input means
- WDM Type
- CWDM offers up to 18 channels; DWDM at 100/50/25GHz offers up to 44/88/160 channels respectively, at increasing equipment cost.
- Channels Needed
- Number of wavelength channels required
- Data Rate per Channel
- Data rate on each wavelength channel (10G, 25G, 40G, 100G, 400G)
- Fiber Pairs
- Number of fiber pairs carrying WDM signals
How this is calculated
Formula
Total BW = Channels × Rate/Channel × Fiber PairsWorked example, using the default values
- Identify Input Parameters4 parametersWDM Type = 2, Channels Needed = 8, Data Rate per Channel = 10, Fiber Pairs = 1 = 4 input(s) provided
- Calculate Usable ChannelsUsable Channels8 = 8
- Calculate Total BandwidthTotal Bandwidth80 = 80
- Calculate Channel SpacingChannel Spacing = 200.8 = 0.8
- Calculate Channel SpacingChannel Spacing = 2500100 = 100
Figures and sources
- ITU-T G.694.2 — CWDM wavelength grid (20nm spacing) (2003) — ITU-T Recommendation G.694.2, "Spectral grids for WDM applications: CWDM wavelength grid", International Telecommunication Union Telecommunication Standardization Sector — defines the 18-wavelength, 20nm-spaced CWDM grid this calculator's CWDM option is built on
- ITU-T G.694.1 — DWDM frequency grid (100/50/25 GHz spacing) (2020) — ITU-T Recommendation G.694.1, "Spectral grids for WDM applications: DWDM frequency grid", International Telecommunication Union Telecommunication Standardization Sector — defines the 100 GHz (0.8nm), 50 GHz (0.4nm), and 25 GHz (0.2nm) DWDM channel grids this calculator's DWDM options are built on
Engine last updated . Checked against 5 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What happens when Channels Needed exceeds the WDM Type's maximum?
Usable Channels is capped at the maximum the selected WDM Type supports -- 18 for CWDM's ITU-T G.694.2 grid, or 44/88/160 for DWDM at 100/50/25GHz spacing under ITU-T G.694.1 -- so requesting more channels than that cap does not increase Total Bandwidth any further. The Channels Fit output flags this directly (1 = your request fits, 0 = it doesn't), so you can tell at a glance whether you need to switch to a tighter-spaced WDM Type or add more fiber pairs instead.
Why does DWDM cost more than CWDM for the same channel count?
DWDM systems pack channels far more tightly (down to 0.2nm spacing versus CWDM's 20nm), which requires much more precise, temperature-stabilized lasers and filters -- reflected here in both the higher relative Cost Per Gbps and the higher MUX + DEMUX Loss figure for the tighter DWDM grids. CWDM equipment is simpler and cheaper per channel, but tops out at far fewer usable channels, so the choice is a real tradeoff between capacity and equipment cost.
How does adding Fiber Pairs change my total capacity?
Total Bandwidth is Usable Channels multiplied by Data Rate per Channel and multiplied again by Fiber Pairs, so doubling Fiber Pairs doubles Total Bandwidth for the same WDM Type and channel plan -- it's a separate, independent multiplier of physical fiber strands rather than another way to add wavelength channels on a single fiber.
What does MUX + DEMUX Loss mean for my link budget?
Every WDM link needs a multiplexer (MUX) to combine channels going out and a demultiplexer (DEMUX) to separate them at the far end, and each introduces insertion loss -- this calculator doubles the typical per-device loss for the selected WDM Type to give you the combined MUX + DEMUX figure. Add that number to your fiber attenuation and connector losses when running a full optical power budget calculation to confirm the receiver still sees adequate signal.
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