How Wi-Fi channels actually work

Channel numbers are a naming scheme over frequencies. Almost every Wi-Fi misunderstanding comes from treating adjacent numbers as separate channels.

Why 1, 6 and 11

2.4 GHz channels are numbered every 5 MHz. A channel occupies about 22 MHz. Those two facts together are the entire explanation: channel 2 sits almost completely on top of channel 1, and only channels five apart clear each other.

That leaves 1, 6 and 11, and nothing else.

Europe permits channels 12 and 13, and it does not buy a fourth clear channel — 11 and 13 still overlap by 12 MHz. The 1/5/9/13 plan some guides recommend accepts overlap rather than avoiding it. That is a reasonable trade in a detached house with no neighbours in range, and a poor one in a block of flats.

Picking channel 3 because "nobody is using it" makes things worse for everyone, including you. It overlaps both 1 and 6, so instead of sharing one channel politely you interfere with two.

Why interference is worse than sharing

Two access points on the same channel take turns. They can hear each other, so they wait, and everybody gets a share.

Two access points on overlapping channels cannot decode each other. They transmit over one another and both sides retry. Sharing a channel costs throughput; overlapping costs far more.

What a wider channel costs

Doubling the width doubles the throughput to one client and halves the number of channels you have to place access points on.

• 5 GHz at 20 MHz — around 25 channels.
• At 80 MHz — six.
• At 160 MHz — two.

In a home with one access point, wide is free and you should take it. In an office with a dozen, wide channels mean they all interfere, and 20 or 40 MHz with more access points beats 80 or 160 with fewer nearly every time. This is why professional deployments often look conservative next to what the hardware advertises.

DFS channels

A large block of 5 GHz is shared with radar. Using it requires the access point to listen and vacate the channel if it detects any — dynamic frequency selection.

It is free extra spectrum and doubles what is available in 5 GHz. Near an airport or a weather station, a detection moves the radio and drops clients, sometimes repeatedly. Worth trying, and worth knowing what to suspect if a network mysteriously stutters at intervals.

6 GHz

Wi-Fi 6E and Wi-Fi 7 add 6 GHz, which is where wide channels stop being expensive because there is finally room for them. Two things to know: only 6E and 7 clients can see it at all, which is a feature since the band starts empty — and Europe allocated roughly a quarter of what the United States did, so the same equipment offers noticeably fewer channels here.

Frequently asked questions

Why can I only use channels 1, 6 and 11?

2.4 GHz channels are numbered every 5 MHz and occupy about 22, so anything closer than five channels overlaps. Only 1, 6 and 11 genuinely clear each other.

Europe allows 12 and 13 — does that give a fourth channel?

No. Channels 11 and 13 still overlap by 12 MHz. The 1/5/9/13 plan accepts overlap rather than avoiding it.

Should I use 160 MHz channels?

At home with one access point, yes. In an office with several, no — there are only two 160 MHz channels in 5 GHz, so they will all interfere. Narrow channels and more access points is the design that scales.

Is channel 3 a good idea because nobody uses it?

No, it is the worst choice. It overlaps both 1 and 6, so instead of politely sharing one channel you interfere with two.

What are DFS channels?

Channels shared with radar, where the access point must vacate if it detects any. They roughly double the available 5 GHz spectrum, at the cost of occasional disruption near airports and weather radar.

Does this replace a site survey?

No. It works from a channel plan and a neighbour list you supply. A real design needs measured signal levels in the actual building, where walls and metal shelving decide the outcome.