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Broadcast Domain Size Calculator

Work out broadcast domain size instantly with clear inputs, formula shown and shareable results.

About Broadcast Domain Size Calculator

Every broadcast is delivered to every host in the VLAN, so aggregate broadcast traffic grows linearly with host count while the load on each individual NIC grows at the same rate. That is why flat networks degrade: at a few thousand hosts, ARP, NetBIOS, mDNS and DHCP chatter alone consume noticeable CPU on every device. Frame overhead of 20 bytes covers the preamble and inter-frame gap on Ethernet.

Formula

Broadcast load

pps = hosts x broadcasts per host; bandwidth = pps x (frame bytes + 20) x 8; every host receives the full pps

Worked example

With the default values below, Broadcast Domain Size Calculator returns Broadcast frames per second in the domain of 1,500.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hosts in the broadcast domainminimum 1
500
Broadcast/multicast frames per host per secondminimum 0.1 pps
3 pps
Average broadcast frame sizeaccepts 64–1,522 bytes
96 bytes

Results

Broadcast frames per second in the domain
1,500.00
Broadcast bandwidth on every link
1.3920 Mbps
Frames each NIC must process per second
1,500.00
Hosts that keep the domain under 1000 pps
333

Step by step

  1. 1Values used
  2. 2Broadcast load
  3. 3Broadcast frames per second in the domain= 1,500.00
  4. 4Broadcast bandwidth on every link= 1.3920 Mbps
  5. 5Frames each NIC must process per second= 1,500.00
  6. 6Hosts that keep the domain under 1000 pps= 333

Assumptions and limits

  • The result is derived only from the 3 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 4 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

How large can a VLAN safely be?

Design guidance usually caps a broadcast domain around 500 to 1000 hosts, which typically corresponds to a /23 or /22. Beyond that, split the VLAN and route between segments.

Does a switch reduce broadcast traffic?

No. Switches flood broadcasts to every port in the VLAN. Only a router or a VLAN boundary stops them.

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