Connection & hardware
How devices sharing your connection split your speed
Your internet connection is a single line, and every device on it shares the same capacity. If another device is streaming video, downloading a file or running a backup, less is left for the test. This usually not only lowers the result but locks the speed at a steady level, because the line is being kept busy by something else.
One line, many devices
The internet coming into your router is a single pipe. Whether two or twenty devices are connected, they all share the same total capacity. While you run a speed test, if another device on the same connection is doing a large download, that pipe is split and the share left for the test shrinks.
Seeing "your speed did not change at all during the test" on your result card can be a sign of this: the line may be held at a steady level by something else.
Things that quietly eat your internet
Often the culprit is not a download you started. Jobs that run by themselves in the background keep the line busy without you noticing:
- Video streaming: a series, film or live stream someone left running; 4K content in particular eats a large share of the line.
- Cloud backups: automatic photo/file backup on phones and computers usually fills the upload direction.
- Updates: operating system, game and app updates download large files in the background.
- Smart-home devices and security cameras: devices that constantly send data are small alone but add up to a noticeable load.
How do you check?
- Review what is running on the other devices on the same connection: a video left open, a download in progress, a backup?
- If you can, pause those jobs temporarily or take those devices off the connection for a few minutes.
- Then run the test again. If the result rose and now fluctuates, the earlier flat result was from shared use.
- To see which device uses how much, check the per-device traffic list in your router's interface or a mesh app.
- If it happens constantly, you can manage the load with QoS in your router, giving certain devices priority.
Is this a problem, or normal?
Sharing is the nature of the internet; it is not a fault. On a line with plenty of capacity, a few devices running at once make no noticeable difference. But when total demand exceeds the line's capacity, everyone slows down. If that happens often, there are two paths: manage the load with QoS, or move to a higher-capacity plan.
How we assess how full the line is during a measurement is laid out in our methodology paper. Measurement methodology
Frequently asked questions
- Why is my speed never changing a sign of a problem?
- On a healthy connection speed moves a little throughout the test. No movement at all can indicate the line is locked at a steady level; the most common reason is another device keeping the line busy.
- Can I measure accurately without turning other devices off?
- If you want to measure your everyday experience, yes: testing under real conditions is useful. But if you want your line's true capacity, pausing the other devices' traffic temporarily gives the cleanest result.
- Is it a Wi-Fi problem or shared use?
- They leave different traces. With a Wi-Fi problem the speed rises and falls; with shared use it stays low but steady. Deal with whichever your result card points to first.
- Does QoS fix this?
- QoS does not share the line equally but prioritises it: it can put your video call ahead of a background backup, for example. If total demand exceeds capacity, QoS manages the delay; but for a permanent shortfall the only fix is more capacity.
Sources
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