Channel width and Wi-Fi speed

Channel width is how much radio spectrum one Wi-Fi link uses at once. It is measured in megahertz (MHz). Common widths are 20, 40, 80, 160, and 320 MHz. A wider channel carries more data per second, if both the router and your device support it.

The link uses the narrower of the two sides

The width in use is the widest one that both the router and the device support. Two examples from maker data:

SideMaximum widthSource
iPhone 17160 MHzApple Platform Deployment
iPhone 17e80 MHzApple Platform Deployment
Intel BE200 laptop chip320 MHzIntel
Nokia WiFi Beacon 6, 5 GHz20/40/80 MHzfccid.io 2ADZRHA0336GA DFS report p5
TP-Link Archer AX55, 5 GHz20/40/80/160 MHzfccid.io 2AXJ4AX55V4 5G report p8

So an iPhone 17 on a Beacon 6 at 5 GHz uses at most 80 MHz (computed: the smaller of 160 and 80).

How width shows up in maker speed figures

TP-Link prints the width next to the speed. For the Archer AX55 it states "5 GHz: 2402 Mbps (802.11ax, HE160)" and "2.4 GHz: 574 Mbps (802.11ax)" (TP-Link). HE160 means a 160 MHz channel in Wi-Fi 6. The 2402 Mbps figure needs a device that also supports 160 MHz.

Width per band

The trade-off

A wider channel uses more spectrum, so it is more likely to overlap a neighbour's network. When it overlaps, the networks share airtime. We have no sourced measurement of how much this costs in a typical home (not yet sourced) . If a 160 MHz setting gives slower or less stable results than 80 MHz in your home, use 80 MHz.

Sources

UNSOURCED count: 1 (overlap cost).