Short answer: leave your router’s channel setting on Auto unless you have a problem. If 2.4 GHz is unreliable, try channel 1, 6 or 11 at 20 MHz width. On 5 GHz, avoid DFS channels if your Wi-Fi keeps dropping. 6 GHz has so much room that channel choice rarely matters there.
What a channel is
Each Wi-Fi band is divided into channels, and your router transmits on one of them at a time. Wider channels carry more data but take up more of the band, which leaves less room for neighbouring networks. For the bands themselves, see Wi-Fi bands explained.
2.4 GHz: only three channels don’t overlap
The 2.4 GHz band is narrow: the FCC rules define it as 2400 to 2483.5 MHz. Its channels are spaced closer together than their width, so neighbouring channels overlap. Cisco’s design guidance notes that, with 11 usable channels in the US, only three don’t overlap: 1, 6 and 11.
That’s why a network on channel 3 interferes with networks on both 1 and 6. If you set 2.4 GHz by hand, pick 1, 6 or 11, and keep the width at 20 MHz so you don’t spill into neighbouring channels.
5 GHz: more room, plus DFS
5 GHz has many more channels, but some are shared with radar. FCC rules require devices using 5.25-5.35 GHz and 5.47-5.725 GHz to detect radar and move off the channel when they hear it; this is called DFS. On these channels, a router may switch channels without warning, briefly dropping connections. If your Wi-Fi keeps dropping on 5 GHz, see why Wi-Fi keeps disconnecting.
6 GHz: plenty of room
In 2020 the FCC opened 1,200 MHz at 5.925-7.125 GHz, and the Wi-Fi Alliance notes the band offers wider channels and less interference from older devices. There’s room even for Wi-Fi 7’s widest channels: Juniper notes three non-overlapping 320 MHz channels in the US. Only Wi-Fi 6E and Wi-Fi 7 devices can use 6 GHz.
When to change the channel
Microsoft lists changing the wireless channel as one way to reduce interference when Wi-Fi is slow.
Channel settings are in your router’s Wi-Fi or wireless settings; see how to log in to your router.