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Uplink Sizing Calculator

Work out uplink sizing instantly with clear inputs, formula shown and shareable results.

About Uplink Sizing Calculator

Uplink sizing starts from peak concurrent demand rather than the sum of port speeds, then adds headroom to keep utilisation near 70 percent. The critical check is failure: with two uplinks in a bundle, losing one doubles the load on the survivor, so a design that runs at 60 percent normally will saturate the moment a link or line card fails.

Formula

Uplink sizing

peak = devices x per-device rate x concurrency; required = peak / 0.7; per uplink = required / uplink count; failure load = required / (uplinks - 1)

Worked example

With the default values below, Uplink Sizing Calculator returns Total uplink bandwidth required of 264.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Devices on the access switchminimum 1
44
Average traffic per deviceminimum 0.001 Mbps
12 Mbps
Share simultaneously at peakaccepts 0.1–100 %
35 %
Uplinks in the bundleminimum 1
2

Results

Total uplink bandwidth required
264.0 Mbps
Bandwidth per uplink
132.0 Mbps
Peak demand before headroom
184.8 Mbps
Utilisation if one uplink fails
200.0%

Step by step

  1. 1Values used
  2. 2Uplink sizing
  3. 3Total uplink bandwidth required= 264.0 Mbps
  4. 4Bandwidth per uplink= 132.0 Mbps
  5. 5Peak demand before headroom= 184.8 Mbps
  6. 6Utilisation if one uplink fails= 200.0

Assumptions and limits

  • The result is derived only from the 4 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 1 decimal place, 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

Does link aggregation give perfectly even distribution?

No. Hashing on flow tuples means a few large flows can land on one member, so a bundle rarely reaches the sum of its members for a small number of heavy flows.

Should uplinks go to different upstream devices?

Yes, with MLAG or equivalent. Two uplinks to the same switch protect against cable and port failure but not against device failure.

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