How to Test Your Internet Speed (and What the Numbers Mean)
"The internet is slow" is the start of most household arguments and most calls to an ISP. Before either, get numbers. Internet speed test measures download, upload and latency with real transfers to Cloudflare, and it's specific about exactly what it sends.
What it talks to
Unlike tools on this site that work entirely in the tab, a speed test has to move data over the network:
- Downloads come from
speed.cloudflare.com/__down. - Uploads go to
speed.cloudflare.com/__up. - The upload data is random bytes generated in your browser with
crypto.getRandomValues. It contains no file, no page content and no identifier from your device. - If Cloudflare's reply names the edge location, the page shows that code and its city.
- The result stays on the page.
Steps
- Press Start test and keep the tab in front.
- Watch download, upload and latency fill in as each transfer finishes.
- Press Stop to end early if you need to.
The three numbers
Latency is measured with several small downloads; the page reports the middle (median) value, so one slow request doesn't skew it. It's what matters most for video calls and gaming: under about 30 ms feels instant, 100 ms and up becomes noticeable.
Download comes from larger transfers. It's what matters for streaming, downloads and browsing.
Upload comes from sending the random bytes. It matters for video calls (your camera), cloud backups and posting videos. Many home plans have much slower upload than download, so don't panic if it's lower.
Getting a reading you can trust
- Test on a cable, then on Wi-Fi. If the cable is fast and Wi-Fi is slow, the problem is the Wi-Fi, not the ISP.
- Stand near the router for a baseline, then test from the room where things feel slow.
- Pause other heavy use: downloads, cloud backups, someone streaming in 4K.
- Test at different times. Evening congestion is real on many networks. Three readings across a day tell you more than one.
- Keep the tab in front. Browsers throttle background tabs, which skews results.
- Restart the router if numbers are far below your plan, then test again.
Interpreting the result
Compare with your plan's advertised speed. Getting 80–90% of the plan on a cable is normal; plans are sold as "up to". Wi-Fi typically gets less, sometimes much less on older routers or through walls. If you consistently get far under the plan on a cable at different times of day, that's the evidence your ISP's support line will ask for. Screenshot it with the time.
Why one test may differ from another
Different speed tests use different servers, different numbers of parallel connections and different durations, so their numbers rarely match exactly. This one uses Cloudflare's network, which has locations in many cities, so it's a good approximation of real-world performance to popular websites. Compare like with like: use the same test when tracking a problem over time.
Privacy
To be precise: the test sends random bytes to Cloudflare and downloads test data from Cloudflare; nothing from your device is in the upload. The page also displays Google ads, as across the site.
FAQ
What does it measure? Download, upload and latency, from real transfers with Cloudflare.
What does it send? Random bytes generated in your browser, to speed.cloudflare.com/__up.
Which server does it use? Cloudflare's speed endpoint; the page shows the edge city when available.
Can I stop a test? Yes, Stop ends the current transfer.
Before you call your ISP, run Internet speed test a few times.
— Alok Kumar Singh