Fibre slow on Wi-Fi but fast on cable: why, and how to fix it
Contents
It is the most common situation with fibre: the cable test shows 200 or 500 Mbps, but the phone in the living room tops out at 60 Mbps. Good news: your line works. The bottleneck is the wireless network.
Why Wi-Fi cannot keep up with fibre
- Radio fades quickly: every wall, especially reinforced concrete, strongly reduces the signal.
- The channel is shared: all devices on a network, plus neighbouring networks on the same channel, share airtime.
- Devices have limits: number of antennas, Wi-Fi standard, transmit power.
- Wi-Fi is half-duplex: it cannot send and receive at the same time on a channel.
Realistic Wi-Fi speeds
| Situation | Common real speed |
|---|---|
| Wi-Fi 4 (2.4 GHz), one room away | 20 to 80 Mbps |
| Wi-Fi 5 (5 GHz), same room | 300 to 600 Mbps |
| Wi-Fi 5 (5 GHz), two walls | 80 to 250 Mbps |
| Wi-Fi 6 (5 GHz), same room, recent device | 500 to 900 Mbps |
| Wi-Fi 6, different floor | 50 to 200 Mbps |
These ranges depend heavily on the home and devices. Above all they show that 1 Gbps fibre is only reachable over a cable or very close to a recent router.
Measure your connection now. Start the test
8 fixes, from simplest to most effective
- Test next to the router: if speed rises, coverage is the issue.
- Use 5 GHz: faster and less crowded, with a shorter range. See 2.4 GHz or 5 GHz.
- Move the router: central, high up, not inside a closed cabinet. See where to put your router.
- Change channel if the interface allows, or leave it on automatic.
- Split or merge the networks: some devices stay stuck on 2.4 GHz when both bands share a name.
- Update your devices' systems and the router firmware.
- Install Mesh or wired access points in larger homes. Comparison: extender, Mesh or powerline.
- Wire fixed devices: TV, console and desktop computer get full fibre speed over Ethernet.
What if speed is low even over cable?
Check the computer's port (it must be gigabit), the cable (Cat 5e or 6) and turn off any VPN. If the problem persists, it comes from the router or the line: see slow internet: causes and fixes.
Sources and further reading
Frequently asked questions
Why does my iPhone or Android not exceed 300 Mbps?
Many phones are limited by their number of antennas and the Wi-Fi standard they support. It is a device limit, not the fibre.
Should I buy a new router?
If your router is old (Wi-Fi 4) and your plan exceeds 100 Mbps, a Wi-Fi 6 router or Mesh brings a clear improvement.
Does Wi-Fi 7 fix the problem?
It improves speed and latency, but only with compatible devices. See our Wi-Fi 6 and Wi-Fi 7 guide.
The SpeedFibre team Guides written and reviewed by a telecom engineer specialised in fibre optics (FTTH), with more than 8 years of hands-on network maintenance and measurement. Editorial policy.
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