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Switch Capacity Calculator

Work out switch capacity instantly with clear inputs, formula shown and shareable results.

About Switch Capacity Calculator

Vendors quote switching capacity as the sum of all port speeds counted in both directions, so a 48-port 25G switch with six 100G uplinks needs 3,600 Gbps of fabric to be non-blocking. The separate forwarding rate in millions of packets per second is what limits small-frame traffic, and it is derived from 64-byte frames plus the 20-byte preamble and inter-frame gap.

Formula

Switch capacity

aggregate = ports x port speed + uplinks x uplink speed; switching capacity = aggregate x 2 (full duplex); forwarding rate = aggregate bits / (64 x 8 + 160) bits per minimum frame

Worked example

With the default values below, Switch Capacity Calculator returns Switching capacity required of 3,600.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Portsminimum 1
48
Port speedminimum 0.001 Gbps
25 Gbps
Uplink portsminimum 0
6
Uplink speedminimum 0.001 Gbps
100 Gbps

Results

Switching capacity required
3,600.0 Gbps
Aggregate port bandwidth
1,800.0 Gbps
Forwarding rate at 64-byte frames
2,678.57 Mpps
Non-blocking requirement
Non-blocking requires a fabric of at least 3600 Gbps full duplex

Step by step

  1. 1Values used
  2. 2Switch capacity
  3. 3Switching capacity required= 3,600.0 Gbps
  4. 4Aggregate port bandwidth= 1,800.0 Gbps
  5. 5Forwarding rate at 64-byte frames= 2,678.57 Mpps
  6. 6Non-blocking requirement= Non-blocking requires a fabric of at least 3600 Gbps full duplex

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

Why is switching capacity double the port bandwidth?

Because each port can send and receive simultaneously at line rate. The marketing figure counts both directions.

Which limit binds first in practice?

Forwarding rate, for traffic dominated by small packets such as voice or DDoS floods. Bandwidth binds for bulk transfer traffic.

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