Free tool
Wi-Fi Channel Planner
Which Wi-Fi channels do not overlap on 2.4 GHz and 5 GHz, how wide to set the channel, and how to lay out access points so they stop interfering with each other.
Suggested channel plan
Wider is not faster when there are neighbours
On 2.4 GHz there are only three channels that do not overlap: 1, 6 and 11. Every other channel sits partly on top of its neighbours, so a site using 3 and 8 is interfering with itself even though the numbers look different. In a building full of other networks, 2.4 GHz is best treated as a compatibility band rather than a performance one.
Wider channels carry more data but hear more noise and leave fewer channels to go around. An 80 MHz channel on 5 GHz gives great speed in an empty building and performs worse than 20 MHz in a crowded one, because every nearby network now collides with yours. For a dense office, narrower and more channels beats wider and fewer almost every time.
Transmit power matters as much as channel choice. Turning every access point to maximum makes them shout over each other and leaves clients clinging to a distant one instead of roaming to the near one. Lower power with more access points produces a faster network than fewer at full power.