Pick the best wifi channel for less interference.
Wifi congestion is not just the number of neighbouring networks — it is how much spectrum each of them overlaps. A wide channel collides with more neighbours than a narrow one, so a 40 MHz channel in a crowded band often performs worse than 20 MHz despite the higher theoretical rate. Weighting neighbour count by channel width, and adding a penalty for weak signal, gives a score that captures both effects.
Weighted congestion score
Width factor = channel width / 20; score = neighbours x width factor x 4 + signal penalty x 3, capped at 100; gain = (current - alternative) / current x 100
Only 1, 6 and 11 in most regions, because they are the only non-overlapping 20 MHz channels. Choosing channel 3 or 9 puts you partially on top of two neighbours' channels instead of sharing one cleanly.
No. Width raises peak throughput but also raises the chance of collision. In a dense apartment building 20 MHz on 2.4 GHz frequently outperforms 40 MHz, while on 5 GHz and 6 GHz there is enough spectrum that 80 MHz is usually safe.
Better than -60 dBm is good, -60 to -70 dBm workable, and below -75 dBm unreliable for anything demanding. Improving signal by relocating the router often helps more than any channel change.