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Link Oversubscription Ratio Calculator

Work out link oversubscription ratio instantly with clear inputs, formula shown and shareable results.

About Link Oversubscription Ratio Calculator

Oversubscription is total access capacity divided by uplink capacity. A 48-port gigabit switch with two 10 gigabit uplinks is 48:20, or 2.4:1 — comfortable, because access ports are rarely all busy at once. Data centre designs target 3:1 or better at the access layer and non-blocking in the spine, while office access layers tolerate 20:1.

Formula

Oversubscription

ratio = (access ports x port speed) / (uplinks x uplink speed)

Worked example

With the default values below, Link Oversubscription Ratio Calculator returns Oversubscription ratio of 2.40. Change any input above and every figure here is recalculated in your browser.

Inputs used

Access portsminimum 1
48
Access port speedminimum 0.001 Mbps
1,000 Mbps
Uplinksminimum 1
2
Uplink speedminimum 0.001 Mbps
10,000 Mbps

Results

Oversubscription ratio
2.40 :1
Total access capacity
48.0 Gbps
Total uplink capacity
20.0 Gbps
Design assessment
Typical access layer ratio

Step by step

  1. 1Values used
  2. 2Oversubscription
  3. 3Oversubscription ratio= 2.40 :1
  4. 4Total access capacity= 48.0 Gbps
  5. 5Total uplink capacity= 20.0 Gbps
  6. 6Design assessment= Typical access layer ratio

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 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

Is oversubscription bad?

No, it is how affordable networks are built. Statistical multiplexing means ports are idle most of the time. It only becomes a problem when many ports are simultaneously busy.

What ratio suits storage or backup traffic?

Much lower, ideally non-blocking. Those workloads drive sustained line-rate transfers where statistical multiplexing does not help.

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