Calculator
Enter counts for your topology. If you are unsure, start with end-device links and hub segments.
Example data table
| Scenario | End links | Inter links | Hub segments | Wi‑Fi domains | Duplex | Total domains | Collision-capable |
|---|---|---|---|---|---|---|---|
| Modern access switch + uplink | 24 | 1 | 0 | 0 | Full | 25 | 0 |
| Mixed wired with one hub segment | 12 | 2 | 1 | 0 | Full | 15 | 1 |
| Legacy half-duplex shared environment | 10 | 1 | 2 | 0 | Half | 13 | 13 |
| Office WLAN plus switched wired | 18 | 1 | 0 | 2 | Full | 21 | 2 |
Formula used
This calculator models collision domains as separate Ethernet segments (microsegments) and shared-media segments:
- TotalDomains = EndLinks + InterLinks + HubSegments + WiFiDomains
- CollisionCapable = if half‑duplex, TotalDomains; if full‑duplex, HubSegments + WiFiDomains.
- CollisionFree = TotalDomains − CollisionCapable
Notes: Switches break up collision domains by port. Hubs repeat frames and create one shared domain. Full‑duplex links do not collide.
How to use this calculator
- Count every direct endpoint-to-switch/router cable as an end-device link.
- Count every uplink between networking devices as an inter-device link.
- Count each hub or shared-media segment once, no matter how many devices attach.
- Select the duplex assumption for your wired point-to-point links.
- Click Calculate, then download CSV or PDF if needed.
FAQs
1) What is a collision domain?
It is the part of a network where frames can collide because devices share the same medium. Hubs create one shared domain, while switches isolate domains per port.
2) Do switches eliminate collisions?
Switches reduce collisions by separating traffic per port. With full-duplex links, collisions are effectively eliminated on those links. Shared segments like hubs can still collide.
3) Why does a hub count as only one domain?
A hub repeats every signal out all ports, so all connected devices share the same media. Because everyone listens and talks on the same segment, it is a single collision domain.
4) What does “collision-capable” mean here?
It counts segments where collisions can realistically occur. Half-duplex Ethernet and hub segments can collide. Full-duplex point-to-point links are treated as collision-free for practical planning.
5) How do I reduce collisions in a LAN?
Replace hubs with switches, ensure links run full-duplex, and avoid shared-media segments. Segmentation with switches and proper cabling reduces contention and improves throughput.
6) What about VLANs and broadcast domains?
VLANs change broadcast domains, not collision domains. A switch port is still its own collision domain. Use VLANs for logical segmentation and security, not for collision control.
7) Does Wi‑Fi have collision domains?
Wi‑Fi is shared radio access, so devices contend for airtime. Collisions can still happen, although the mechanism differs from classic Ethernet. This tool models each WLAN cell/channel as one contention domain.
8) Why count links instead of devices?
Collision domains are defined by segments and media, not by device totals. A switch isolates domains per port link, while a hub merges many devices into one shared segment.