Why do speed tests give different results? Speedtest vs Fast.com vs your provider's test
One site says 480 Mb/s, another says 310, your provider's checker says 520 and your phone says 140. They can all be telling the truth: each one measures a slightly different path, in a slightly different way.
What each test actually measures
| Test | Tests to | Method | Tends to read |
|---|---|---|---|
| Ookla Speedtest | A nearby server it picks (you can change it), often hosted by your own provider | Several connections in parallel | Highest; close to your line's capacity |
| Fast.com (Netflix) | Netflix's own video servers, many placed inside providers' networks | Several connections, download first | Close to what streaming services can get |
| Google "Run speed test" (M-Lab NDT) | Measurement Lab servers | A single connection | Lower on fast or distant connections; closer to one big download |
| Cloudflare (speed.cloudflare.com) | Cloudflare's network | Many small and large transfers, plus latency while loaded | Handy for spotting lag under load (bufferbloat) |
| Your provider's checker | A server inside its own network | Varies | Usually highest, because the traffic never leaves their network |
None of them is "the real one". A test to a server in your own town says how fast your line is; a test to a server across the world says how fast that particular route is. Both are true.
Things on your side that cap the number
- Wi-Fi. The biggest one. Distance, walls and the 2.4 GHz band can take a 500 Mb/s line down to 50. A phone on Wi-Fi testing far lower than a laptop on a cable is normal.
- The device. Older phones, budget laptops and some TVs top out well below gigabit on Wi-Fi. Many TVs, older consoles and laptops have a 100 Mb/s network port, which tests at about 94 Mb/s whatever your plan is.
- The cable and port. A damaged cable or a router port that has dropped to 100 Mb/s gives the same 94 Mb/s ceiling. Check the link speed in your network settings (it should say 1 Gbps for a plan over 100 Mb/s), and see Ethernet cables.
- Everyone else at home. A game update or cloud backup on another device takes part of the line while you test.
- VPNs and security software reroute or inspect traffic and often slow it down.
- Browser vs app. A busy browser with lots of tabs can under-read on very fast lines; the test's own app can read a little higher.
Why even the best test reads below your plan
Advertised speeds are line rates. Part of every packet is addressing and checking (protocol overhead), so a perfectly healthy 100 Mb/s line usually tests around 92-95 Mb/s. Results within about 10% of your plan on a cable mean the line is fine. Watch the units too: 100 Mb/s (megabits) is about 12.5 MB/s (megabytes) in a download window; see Mbps vs MB/s.
Why the same test changes through the day
Parts of the network are shared with other homes, and between about 7 and 11 pm they're busiest. A drop only in the evening, on a cable, is congestion at your provider rather than a fault at home: see internet slow in the evening and contention ratios.
A test you can trust (and show your provider)
- A laptop or computer on a cable plugged straight into the router; check the link says 1 Gbps if your plan is over 100 Mb/s.
- Pause other devices, downloads, backups and VPNs.
- Run two different tests (for example Speedtest and Fast.com), twice each.
- Repeat early morning, afternoon and about 9 pm on two or three days, and note download, upload and ping.
- Compare with your plan and any minimum guaranteed speed in your contract, not just the headline figure.
If every cable test is far below the plan at every hour, report it as a fault. If it's fine on the cable but poor on Wi-Fi, improve the Wi-Fi rather than the plan. To check whether your plan is enough in the first place, try the broadband speed calculator.
Related
Internet slow in the evening · How much broadband speed do I need? · Mbps vs MB/s · Lag when someone downloads (bufferbloat) · Which Ethernet cable? · Interactive: the water-balloon speed test race (Wirebook) · Interactive: how shared pipes fill up (Wirebook)
Questions
Which speed test is the most accurate?
They're all accurate for what they measure. Ookla Speedtest to a nearby server shows your line's capacity, Fast.com shows what streaming gets, and Google's single-connection test is closer to one big download. Use two tests on a cable for a fair picture.
Why is Fast.com slower than Speedtest?
Fast.com tests to Netflix's servers rather than a nearby test server, so it can read lower if the route to Netflix is busy. If films stream fine, the lower figure is usually still plenty.
Why does my provider's speed test show more than other sites?
It tests to a server inside its own network, so the traffic never crosses the busier links to the rest of the internet. That shows your line is fine, but not necessarily what every website gets.
Why does my phone get a lower speed test than my laptop?
The phone is almost always on Wi-Fi, further from the router, and limited by its own Wi-Fi hardware. Test on a laptop with a cable to see the line's real speed.
Why do I always get about 94 Mb/s on a faster plan?
Something in the path runs at 100 Mb/s: the device's network port, a damaged cable or a router port. Check the link speed in network settings and try another cable and port.
Published · updated .