Why your Wi-Fi speed is below your plan speed

Your internet plan names one number, such as "1 Gig". A speed test over Wi-Fi almost always shows a lower number. This page lists the main reasons, in the order you should check them. Each number on this page has a source next to it.

1. Some bits carry headers, not your data

Every packet carries Ethernet, IP, and TCP headers. Those bytes use line capacity but are not your download. RFC 6349 shows the calculation for standard 1500-byte packets: the most TCP data a 1000 Mb/s Ethernet link can carry is 949.2 Mb/s (RFC 6349 §4.1.1).

So a perfect wired test on a 1 Gb/s port tops out near 949 Mb/s, about 94.9% of line rate (computed: 949.2 / 1000). AT&T states an "estimated max throughput of 940Mbps" for 1 Gbps Ethernet ports (AT&T broadband performance). See What "94% of line rate" means for the full arithmetic.

2. The port or cable is slower than the plan

If your router's WAN port or the port your computer uses is 1 Gb/s, a 2 Gig plan cannot reach that computer at more than about 949 Mb/s (computed, from RFC 6349 above). Check the maker's spec page for your router's ports. For example, Nokia lists the WiFi Beacon 6 WAN port as "One 10/100/1000 Base-T interface" (Nokia), so that unit cannot pass more than 1 Gb/s on its wired WAN.

3. Your device has fewer antennas than the router

A Wi-Fi link runs at the speed of the weaker side. Most phones and laptops have two spatial streams. Apple lists 2 streams for every current iPhone, iPad, and Mac in its Wi-Fi table (Apple Platform Deployment). Intel lists its AX210 and BE200 laptop chips as 2x2 (Intel AX210, Intel BE200). A router advertised as "12 streams" still talks to a 2-stream phone with 2 streams.

4. The router's speed rating is a sum of all bands

A name like "BE19000" adds up the maximum rates of every band. TP-Link lists the Archer BE800 as 6 GHz: 11520 Mbps, 5 GHz: 5760 Mbps, 2.4 GHz: 1376 Mbps (TP-Link). Those three add to 18656 Mbps (computed), which the maker rounds into the class name. A single phone or laptop connects with its own streams and widths, so it does not see the sum.

5. The channel is narrower than the maximum

Wider channels carry more data. A device's top width is set by the device and the router together. Apple lists 80 MHz as the maximum for iPhone 16e and iPhone 17e, and 160 MHz for iPhone 17 (Apple Platform Deployment). See Channel width and speed.

6. Distance, walls, and neighbours

Signal falls with distance and through walls, and the link drops to a slower rate. Neighbouring networks on the same channel share airtime with you. We have no sourced figure for how much a given wall costs, so this page gives none (not yet sourced) .

7. The test itself

A test to a far server, a test during peak hours, or a test while other devices stream will read low. See How to run a fair speed test.

What to check, in order

  1. Run a wired test from a computer with a port at least as fast as your plan. If it reads near the RFC 6349 ceiling for that port, the line is fine.
  2. Read your router's and device's spec pages for port speed, streams, and widths.
  3. Retest over Wi-Fi close to the router on 5 GHz or 6 GHz.

Sources

UNSOURCED count: 1 (wall loss figure).