1, 6, and 11 don't overlap. Every other 2.4GHz pair does.

Two routers sitting three channels apart on 2.4GHz are not on different channels in any way that matters. A Wi-Fi channel is not a number on a dial; it is a roughly 22 MHz wide hump of energy, and the channel spacing is only 5 MHz. So channel 1 and channel 3 slam directly into each other, and channel 1 and channel 4 still clip. The only way to fit three non-overlapping networks into the 2.4GHz band is to space them far enough that their humps miss entirely, which lands you on 1, 6, and 11. That is the whole reason those three numbers are the ones every forum repeats, and it is a fact you can see instead of memorize.

Channel Clear is a free page that finds the clearest channel for your own router. You already have the input: open your phone's Wi-Fi settings and you are looking at a list of neighbor network names and their channels. Channel Clear asks for exactly that, nothing else, and does the part that actually takes knowledge: the channel-width and adjacent-channel overlap math. Then it points at the gap.

The chart is the reasoning

Every other Wi-Fi analyzer I have used ends at a verdict. "Channel 6 is congested." Fine, but why, and by how much, and what should I do about it? Channel Clear models each network you enter as a raised-cosine energy curve centered on its channel, about as wide as a real Wi-Fi signal (22 MHz on 2.4GHz, 20 MHz on 5GHz), tapering to zero at roughly twice its half-width. That taper is the important bit. It means two networks a few channels apart register as partial interference, a curve that leans into its neighbor, rather than the binary "channel used / channel free" that a lookup table gives you. As you add each network, the spectrum redraws live and you watch the humps stack up. The congested part of the band is just where the curves pile highest.

The recommendation falls straight out of that model. For every candidate channel, Channel Clear sums the overlap of your entered networks against a router placed there, and picks the channel with the least total. Ties break toward the lower channel number, so the answer is stable and explainable rather than flickering between two equally-good spots. An amber marker drops onto the winning channel. On a clean-ish 2.4GHz block with neighbors on 1 and 6, the arrow lands on 11, and now you can see it earned that, it did not just recite folklore.

2.4GHz and 5GHz never interfere with each other and have different widths and spacing, so the two bands are modeled as fully independent, each with its own chart and its own recommendation. Flipping the band toggle re-scopes everything without losing what you typed on the other side.

Why you type it in

Here is the honest limitation, and it is a browser limitation, not a lazy one: a web page cannot scan Wi-Fi. That capability is gated behind native APIs and location permission on purpose, which is exactly why every "analyzer" in the app store wants an install and a permission grant before it shows you a single bar. Manual entry is the price of staying a URL instead of an install. Typing in three to five networks off your phone takes under a minute, and in exchange nothing you enter ever leaves the browser: no account, no backend, no network call, all the math and drawing run client-side on a plain static page. Your spectrum even lives in the link, so you can copy a URL that reproduces the exact chart or reload and pick up where you left off.

Try it

Open Channel Clear, pick the band, and add the first two or three networks you can see in your phone's Wi-Fi list, name and channel. Watch the curves stack and the amber marker settle on the clearest channel, then go set your router there. The overlap model and its property-based tests are on GitHub if you want to check the math.