What is jitter?
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Jitter is how much your latency changes from one moment to the next. If every request takes 20 ms, jitter is zero. If they take 15, 60, 20 and 45 ms, jitter is high. It is measured in milliseconds, and lower is better.
Why jitter matters
Video calls, voice calls and online games send a steady stream of small packets and expect them to arrive at an even pace. When the delay keeps changing, apps either wait longer (adding lag) or play what they have (causing robotic voices, frozen video and characters that jump around). Streaming video is barely affected, because it buffers several seconds ahead.
What is good jitter?
| Jitter | Gaming (HowFast rating) | Video calls (HowFast rating) |
|---|---|---|
| 5 ms or less | Great | Great |
| Over 5 to 10 ms | Good | Great |
| Over 10 to 20 ms | Fair | Good |
| Over 20 to 30 ms | Poor | Fair |
| Over 30 ms | Poor | Poor |
These are the thresholds HowFast uses (rubric version 1). See speed by usage for the other metrics in each rating.
How jitter is calculated
HowFast sends a series of small requests while the line is idle and records the latency of each, in the order they were sent. Jitter is the average difference between each request and the one before it:
jitter = average of |latency₂ − latency₁|, |latency₃ − latency₂|, …
This is the same definition Cloudflare’s open-source speed test engine uses, so numbers are comparable between the two. Some tools report the standard deviation of latency instead, which gives a different number for the same connection. The test needs at least five valid measurements to report jitter. More on the methodology page.
What causes jitter
- Wi-Fi, especially with a weak signal, interference from neighbours’ networks, or many devices on the same channel.
- A busy connection. Uploads and downloads fill queues in your router unevenly, which makes delay swing. This is closely linked to bufferbloat.
- Mobile networks, where signal and congestion change constantly.
- Overloaded or old routers and powerline adapters.
- Background activity on the device itself, such as updates and cloud sync.
How to reduce jitter
- Use a cable for the device you call or game on. This fixes most Wi-Fi jitter immediately.
- Move closer to the router, or use the 5 GHz or 6 GHz band, which is usually less crowded than 2.4 GHz.
- Turn on SQM or QoS on your router so calls and games aren’t stuck behind large transfers.
- Pause backups and updates during important calls.
- Restart or replace an old router if jitter stays high on a cable connection with nothing else running.
- If jitter is high even on a cable with a quiet network, test at different times and keep the results. Persistent jitter at the line level is something your provider should look at.
Frequently asked questions
Is jitter the same as packet loss?
No. Jitter is variation in delay; packet loss is data that never arrives. They often appear together on poor Wi-Fi or congested lines, and both disrupt calls. See packet loss.
Why does the HowFast result say “Your connection is uneven”?
That summary is shown when jitter is the metric holding your gaming or video-call rating at Fair or worse, unless a more important issue, such as very slow download or bufferbloat, is found first. The order of the rules is on the methodology page. A wired connection often helps.