What bufferbloat is
When a download or upload fills your connection, the router and modem queue the extra packets in memory buffers. If those buffers are too large and badly managed, every packet waits in line: your ping can jump from 15 ms to 200 ms or more as soon as someone starts a backup, a game update or a 4K stream. That delay is bufferbloat. Speed looks fine, yet video calls freeze and games lag.
How this test measures it
The test runs in three phases:
- Ping at rest: small packets on an idle line, the value most speed tests display.
- Ping during download: measured while the test saturates the download.
- Ping during upload: measured while the test saturates the upload.
Under the result, the Latency under load line shows the highest of the two loaded values and how many milliseconds it adds to the ping at rest. The game, video call and streaming grades take that increase into account.
How to read your result
| Increase under load | Verdict | What you will notice |
|---|---|---|
| Less than 30 ms | Stable (A or B) | Nothing: calls and games stay smooth during transfers |
| 30 to 100 ms | Slight bufferbloat | Small spikes in games and calls when the line is busy |
| More than 100 ms | Severe bufferbloat | Lag, frozen video and voice cuts as soon as someone downloads |
Run the test twice: once on an idle network, once while another device streams video. Results vary between runs, so look at the trend rather than one number.
Measure your connection now. Start the test
Which connections suffer most
- Cable and DSL: upload is small, so it fills quickly and the queue grows. Upload bufferbloat is the most common case.
- 5G home internet and satellite: the radio link adds its own variable queues.
- Fibre: usually the best, but a router overwhelmed by a gigabit line, or a busy Wi-Fi network, can still add delay.
How to fix bufferbloat
- Turn on smart queue management (SQM) on your router if it has it. The setting may be called Smart Queue, QoS, Adaptive QoS or SQM with fq_codel or CAKE. It reorders packets so that small, urgent ones are not stuck behind large transfers.
- Set the SQM limits slightly below your measured speeds, around 90 to 95 % of the download and upload you get over cable. The queue then forms in your router, which manages it well, instead of in the modem.
- Use Ethernet for the console or PC that needs low latency: Wi-Fi adds its own queues.
- Schedule heavy transfers: cloud backups and game updates can run at night.
- If your provider's router has no such option, a separate router with SQM placed behind it (with the provider's box in bridge mode where possible) solves most cases.
Then test again and compare the Latency under load line. For the basics of ping and jitter, read ping, latency and jitter explained; for gaming, lower your ping.
Frequently asked questions
Is bufferbloat my provider's fault?
Usually not. The queue that grows is most often in your own router or modem. Smart queue management on your side fixes most cases, whatever the provider.
Does a faster plan fix bufferbloat?
It can reduce it, because the line saturates less often, but it does not cure it. A slow line with good queue management feels better than a fast line without it.
Does SQM reduce my speed?
Slightly: you set it a little below your real speed, so you lose about 5 to 10 % of throughput in exchange for stable latency. For calls and games, the trade is almost always worth it.
