Internet speed explained
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Internet speed is how much data your connection can move each second. A speed test measures it in two directions: download, from the internet to you, and upload, from you to the internet. Both are shown in megabits per second (Mbps).
Download speed
Download speed decides how quickly things arrive: video streams, web pages, app and game updates, files. It is the number internet plans advertise, and usually the larger of the two.
HowFast measures it by downloading files of increasing size from our test server and timing each one. The headline is the 90th percentile of the valid transfers: a high but repeatable value that shows what the connection sustains once it is up to speed. Very short transfers and the first “warm-up” transfer are left out because they understate speed. The details are on the methodology page.
Upload speed
Upload speed decides how quickly you can send things: your camera and voice on a video call, photos to the cloud, files to colleagues, a live stream. Many cable and DSL plans upload far more slowly than they download, so upload is often the reason calls break up while streaming works fine.
Mbps, MB/s and Gbps
- Mbps (megabits per second) is the unit for connection speed.
- MB/s (megabytes per second) is what download managers and game launchers often show. One byte is eight bits, so divide Mbps by 8 to get MB/s. A 400 Mbps connection downloads at up to about 50 MB/s.
- Gbps is 1,000 Mbps.
Why the result can be lower than your plan
A test result is what reached your browser at that moment. Common reasons it falls short of the advertised figure:
- Wi-Fi. Walls, distance, older devices and neighbouring networks often limit speed more than the plan does. A cabled test is the fair comparison.
- Other activity. Streams, backups, updates and other people on the network share the same line.
- Your device. Old phones, laptops in power-saving mode, and browsers busy with many tabs can’t always keep up with fast connections.
- One connection. The test measures what a single browser connection achieves, because that is what most apps use. On plans above about 1 Gbps one connection may not fill the line; Detailed mode adds a separate four-connection figure.
- Busy hours. Shared networks, especially cable and mobile, slow down at peak times.
- VPNs. A VPN sends traffic through another server, which adds distance and can cap speed. The result then describes the VPN path, and HowFast notes this when it can tell.
- Plan overhead. Advertised speeds are usually “up to” figures measured before some network overhead.
Speed isn’t everything
Two connections with the same speed can feel very different. Latency (the delay before data starts arriving), jitter (how much that delay varies) and bufferbloat (extra delay when the line is busy) decide how responsive games, calls and browsing feel. A HowFast result shows all of them alongside speed:
How to get an accurate reading
- Close other apps and pause large downloads.
- Test on a cable connection first, then on Wi-Fi where you use it.
- Run two or three tests and at different times of day. The history panel keeps your past results in your browser so you can compare.
- If you contact your provider, a set of cabled results from different times is much more persuasive than a single Wi-Fi test.
Frequently asked questions
Which matters more, download or upload?
For watching and browsing, download. For video calls, working from home, gaming uploads and backups, upload matters too, and it is often the weaker of the two.
Why do different speed tests give different results?
They use different servers, different numbers of connections and different ways of summarising the samples. Tests that open many connections at once usually show higher numbers on fast lines. Our methodology explains exactly how HowFast does it.
Does a speed test use a lot of data?
A Standard HowFast test uses up to about 200 MB, and the Reduced data mode up to about 25 MB. The dashboard shows the maximum before you start and counts the data as it goes.