When you unbox and set up your new router in North America, you’re given the option of using no fewer than 11 different channels on the 2.4GHz band. That’s a lot of options for you to choose from, but in reality, you should ignore the vast majority of them.

In fact, out of those 11 different channels, a total of eight of them should be ignored right out of the gate. They’re a terrible choice and can actively downgrade your home network’s performance. But why that’s the case and knowing which options you should choose is an interesting lesson in how Wi-Fi actually works, and why those 11 channel options should really be just three.

The physics of channel overlap

And the 20MHz rule

To understand why eight of those 11 channels should be ignored, we must first look at how Wi-Fi signals are transmitted and received by our devices. While the Federal Communications Commission (FCC) allows for 11 individual channels across the 2.4GHz spectrum, those channels are spaced just 5MHz apart. And a standard Wi-Fi transmission requires a width of 20MHz in order to carry data from the sending device to the receiving one. To complicate matters further, the 2.4GHz band is just 100MHz wide.

Because a 20MHz signal uses four times as much space as the 5MHz space between the channels, each one bleeds into those on either side of it. If you choose channel three, for example, it’ll actually also include channel one through channel five. That means that choosing one of those channels risks cross-channel interference from other routers in your neighborhood, which, in turn, impacts performance.

While channels one, six, and 11 (all primary channels) also overlap with other channels, they are the only ones that do not overlap with any of the primary channels. But if routers should be set up to use just three channels, it’s likely your router and those of your neighbors will wind up sharing the same channel. Thankfully, that isn’t the problem it might seem to be.

Co-channel cooperation

Avoiding the chaos

The next important factor to consider is the difference between Co-Channel Interference (CCI) and Adjacent-Channel Interference (ACI.)

When two routers in the same physical space use the same channel, they experience CCI. The good news is that the router and the Wi-Fi protocol itself were engineered to wait their turn rather than competing with another router on the same channel. This can have the impact of slower performance during peak usage, but the data stream remains intact, and the connection remains stable as a result.

Things work very differently when using a channel that overlaps with a neighbor’s router, though. If your router uses channel three but your neighbor uses channel one or channel six, ACI occurs. But because the channels only partially overlap, your router cannot properly decide which part of the transmission is your network, and which isn’t. The result is that your neighbor’s router adds noise to the transmission.

The knock-on effect is a battle of wills between the two routers. They keep ratcheting up the signal to try to shout over one another. This causes latency spikes and an overall degraded connection for users of both routers.

Ultimately, the better approach would be for both routers to use the same channel to allow the underlying protocol to do its job, allowing your router to better understand which data to ignore.

The 11-channel myth

It just won’t go away

With all of that said, the obvious question is why do routers come with 11 channels if only three of them should be used? It all comes down to a need for backward compatibility.

The 2.4GHz band was designated as part of the unlicensed Industrial, Scientific, and Medical (ISM) radio band when early wireless networking standards were being decided upon in the late 1990s. Early protocols like the original 802.11 DSSS (Direct-Sequence Spread Spectrum) used different channel widths and modulation schemes than the new, more modern 802.11n or 802.11ax standards. The FCC defined 11 frequencies across the 2.4GHz spectrum, and that was the end of that.

Globally, regulatory rules around the 2.4GHz band vary considerably. Europe and most of the world allow for 13 channels in the 2.4GHz band, leaving one, five, nine, and 13 as non-overlapping options. Japan even adds a 14th channel to the mix. But chipsets are manufactured with a global market in mind, with hardware makers sticking to the underlying 5MHz steps between channels. Restricting a router sold in North America to only channels one, six, and 11 would require extra work that vendors simply choose not to do.

Stick to the holy trinity

Choose one, six, or 11

It might be tempting to choose a channel as far away from those of your neighbors’ routers as possible. But that attempt to escape wireless congestion can be a trap that ultimately hampers your Wi-Fi performance rather than helps it.

All of this is to say that most routers in North America should be set up to use channels one, six, or 11. If you live in the middle of nowhere and yours is the only Wi-Fi signal in town, you might be OK choosing one of the others, but that doesn’t apply to most people or, indeed, most routers.