The test finishes and a set of numbers appears. The big number at the top gets all the attention, but the real explanation for your problem is often a small number next to it. This article goes through each one, what is normal, and when you should worry.
Download
How much data reaches your device per second, in megabits (Mbps). This is the number providers sell, and it decides how fast pages open, how fast files download and the highest video quality you can watch without buffering.
How to judge it: compare it with your plan, not with other people's numbers. On a cable, 85–95% of the plan is a good result. On Wi-Fi, the result depends heavily on location and device.
Upload
What your device sends to the internet. You see its effect in video calls, posting photos and clips, backups and live streaming.
On ADSL and many cable and mobile connections, upload is much lower than download, sometimes a tenth or less, and that is part of how the service is designed, not a fault. Fibre usually gives much higher upload, sometimes equal to download.
When it is a problem: if your video freezes in meetings while other people's audio is clear, upload is usually the cause. Less than 3 Mbps upload will struggle with an HD video call, especially if someone else at home is uploading.
Ping
The time a small message takes to reach the server and come back, in milliseconds. It measures responsiveness, not transfer speed.
| Ping | Rating |
|---|---|
| Under 20 ms | Excellent, usually fibre and a nearby server |
| 20–50 ms | Very good for everything |
| 50–100 ms | Acceptable, but noticeable in fast games |
| Over 100 ms | Clear delay in games and calls |
Ping depends heavily on distance. Light in fibre needs about 5 ms per 1,000 km each way, so 10 ms there and back. Ping to a server 3,000 km away can therefore never be much below 30 ms, however fast your line is.
Latency during download and upload
These two numbers set a good test apart. We measure ping while the line is fully loaded, because that is the real situation when someone at home is watching video while you game or take a call.
If ping rises from 20 to 300 during the download, that is called bufferbloat, and it is the most common cause of "mysterious" lag on fast lines. We explain it in detail, with the fix, in this article.
Rule of thumb: an increase of less than 30 ms over idle ping is excellent. More than 100 means the router needs better queue management.
Jitter
How much ping changes from one reading to the next. Readings of 20, 21, 19, 22 mean very low jitter. Readings of 20, 85, 18, 140 mean high jitter, even if the average looks reasonable.
Voice and video calls are very sensitive to jitter because they need data to arrive at a steady rhythm. Apps try to compensate by delaying audio slightly, but once jitter goes past roughly 30 ms, voices start to break up or sound robotic.
Most common cause: weak or congested Wi-Fi. Test over a cable; if jitter drops sharply, you know where the problem is.
Packet loss
The share of data that was sent but never arrived. On a healthy connection it should be zero or very close to it.
- For downloads and browsing, the protocol resends what was lost, so you only notice slowness.
- In games and calls there is no time to resend, so it shows up as players jumping around or missing words in a call.
When to worry: any steady figure above 1% deserves investigation. On Wi-Fi, interference may be the cause; on a cable, it is usually a damaged cable, a loose connector or a problem on the provider's line, and that last one is for the provider to fix.
Putting the picture together
| What you see | Most likely explanation |
|---|---|
| Low download, everything else normal | Wi-Fi, an old device, or evening congestion |
| Very low upload and your video freezes in meetings | The plan itself, or another device uploading in the background |
| Good idle ping, very high ping during download | Bufferbloat in the router |
| High jitter on Wi-Fi only | Interference or weak signal |
| Steady packet loss on a cable | A fault in the cable or the provider's line |