VLAN Calculator
Plan VLAN IDs, subnets and trunking assignments across switches.
About VLAN Calculator
VLANs (Virtual LANs, IEEE 802.1Q) split a single physical switch into multiple isolated broadcast domains, each identified by a VLAN ID from 1–4094. Planning VLAN capacity means dividing the switch's access ports (after reserving trunk/uplink ports for tagged inter-switch traffic) evenly across the number of VLANs needed, and checking that each VLAN's device count fits within its allotted ports — since every device in a VLAN shares the same broadcast domain and Layer 2 traffic isolation.
Formula
Access ports per VLAN
ports_per_vlan = floor((total_ports − trunk_ports) / number_of_vlans)
- T
- Total switch ports
- k
- Trunk/uplink ports reserved
- v
- Number of VLANs
Worked example
With the default values below, VLAN Calculator returns Access Ports per VLAN of 11. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Total Switch Ports Availableminimum 1
- 48
- Number of VLANsaccepts 1–4,094
- 4
- Trunk Ports Reservedminimum 0
- 2
- Devices per VLANminimum 1
- 10
Results
- Access Ports per VLAN
- 11
- Access Ports Available
- 46
- Unallocated Ports
- 2
- Total Devices Across All VLANs
- 40
- VLAN ID Space Used
- 0.098%
Step by step
- 1Values used
- 2Access ports per VLAN
- 3Access Ports per VLAN= 11
- 4Access Ports Available= 46
- 5Unallocated Ports= 2
- 6Total Devices Across All VLANs= 40
- 7VLAN ID Space Used= 0.098
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 or compounding frequency into account.
- Figures are rounded for display to 3 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
What is the valid range of VLAN IDs?
IEEE 802.1Q defines VLAN IDs from 0 to 4095, but 0 and 4095 are reserved for special use, leaving 1–4094 (4094 usable VLANs) for normal configuration. VLAN 1 is also often reserved as the default/native VLAN by convention.
Why do trunk ports need to be reserved separately?
Trunk ports carry tagged traffic for multiple VLANs between switches (or to a router) and aren't assigned to a single VLAN's access port pool, so they must be subtracted from the total before dividing remaining ports among VLANs.
Why does VLAN size matter for broadcast traffic?
All devices in the same VLAN share one broadcast domain — a broadcast frame (like an ARP request) is delivered to every device in that VLAN. Larger VLANs mean more broadcast traffic reaching more hosts, which can affect performance if a VLAN grows too large.
What if I need more devices in a VLAN than I have ports for?
You'll need additional switches connected via trunk ports (extending the same VLANs across switches) or a higher port-density switch. The trunk link carries the VLAN-tagged traffic between switches so the VLAN's broadcast domain spans both.