Wi-Fi Channel & Capacity Planner

2.4 GHz channels are numbered every 5 MHz and occupy about 22. That is the whole explanation. Channel 2 sits almost entirely on top of channel 1. Only channels five apart clear each other, which 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 suggest accepts overlap rather than avoiding it, which is a reasonable trade in a quiet area and a poor one in a block of flats.

Doubling the channel width halves the number of channels. A wider channel carries more per client and leaves fewer places for your other access points to go. In a dense deployment, narrow channels and more access points beat wide channels and interference nearly every time — 20 or 40 MHz in 5 GHz is a common professional default despite the hardware supporting more.

6 GHz is where wide channels stop being expensive, because there is enough spectrum for them. Note that Europe allocated roughly a quarter of what the United States did, so the same equipment offers noticeably fewer channels here.

DFS channels require the access point to listen for radar and vacate if it hears any. That is free extra spectrum, and near an airport or a weather station it can mean clients being disconnected while the radio moves.

What this is not

These are planning figures from a channel plan and a neighbour list you supply. Real Wi-Fi design needs measured signal levels — a survey with an instrument in the actual building, where walls, lift shafts and the metal shelving nobody mentioned decide the outcome. This narrows the question; it does not answer it.