Plan a 2.4 GHz deployment against the only three non-overlapping channels, and see the co-channel contention it creates.
The 2.4 GHz band is 83.5 MHz wide, which fits only three 20 MHz channels without overlap, so every extra radio has to share one of them. Because co-channel radios take turns rather than transmitting simultaneously, their airtime demands add up until the channel is fully busy. 2.4 GHz is the band legacy IoT and guest devices land on, and leaving it enabled on every AP is the most common cause of a Wi-Fi network that tests well and performs badly.
2.4 GHz Channel
radios per channel = 2.4 GHz radios ÷ usable channels; channel utilisation = radios per channel × airtime demanded per radio.
radios per channel = 2.4 GHz radios ÷ usable channels; channel utilisation = radios per channel × airtime demanded per radio. The 2.4 GHz band is 83.5 MHz wide, which fits only three 20 MHz channels without overlap, so every extra radio has to share one of them. Because co-channel radios take turns rather than transmitting simultaneously, their airtime demands add up until the channel is fully busy.
2.4 GHz is the band legacy IoT and guest devices land on, and leaving it enabled on every AP is the most common cause of a Wi-Fi network that tests well and performs badly.
This calculator takes 4 inputs: 2.4 GHz radios in the coverage area, Non-overlapping channels in your regulatory domain, Using 40 MHz channel bonding, Airtime demanded per radio. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.