Bufferbloat Test: What Your Ping Does Under Load
A fast connection that feels terrible in games is almost always this: under load, your router holds on to traffic instead of dropping it, and your round trip goes from 20 ms to several hundred. Speed tests never see it, because the bytes do arrive — they just arrive late. This measures the gap.
Connecting…
At rest: —
Download
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- Under load
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- Worst 5%
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- Throughput
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Upload
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- Under load
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- Worst 5%
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- Throughput
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The throughput figures are here to show the load was real enough to fill the line. They are not a speed test result, and this page is not trying to be one.
Open the shareable resultWhat bufferbloat actually is
Every link between you and the internet has a queue. When more traffic arrives than the link can carry — a game update downloading, a cloud backup running, a console syncing — the equipment at the narrow point decides what to do with the excess. A well-behaved device drops a little of it, which is the signal that tells senders to slow down. A bloated one accepts all of it into a queue that can hold seconds of traffic.
Nothing is lost, so a speed test still reports the full line rate. But every packet now waits behind everything already in the queue, including the ones your game is sending. That is why the symptom is so specific: the connection is fine when nothing else is happening and unplayable the moment somebody starts a download.
How this test measures it
- Five seconds at rest. A baseline round trip to the same server the load will come from. Every number below is measured against this one.
- Ten seconds of download. Our server sends as fast as your connection will take it, while the round trip keeps being measured on the same connection — so the probes travel through the queue the load is filling.
- Two seconds to settle, so the queue drains before the next phase. Without it, the download's backlog would be charged to the upload.
- Ten seconds of upload. The same, in the other direction. On most home connections this is the direction that bloats, because the upstream is the narrower half.
The grade is the increase in median round trip, and the overall grade is the worse of the two directions rather than their average. A line whose download is clean and whose upload collapses is a line you cannot play on, and averaging would hand it a passing letter.
What the grades mean
| Grade | Added latency | What it means |
|---|---|---|
| A+ | under 5 ms | No measurable buffering. Voice chat, streaming and a game can share this line without noticing each other. |
| A | 5-30 ms | Slight buffering. You will not feel it in a game. |
| B | 30-60 ms | Noticeable buffering. A large download in the background will cost you the occasional trade. |
| C | 60-200 ms | Heavy buffering. Anything else using the line makes the game feel rubber-bandy. |
| D | 200-400 ms | Severe buffering. The line is unusable for a game while anything else is downloading. |
| F | 400 ms or more | The line collapses under load. This is what "my internet is fast but games lag" looks like when it is measured. |
How to fix it
Bufferbloat is a queue management problem, not a bandwidth problem, and buying a faster line usually does not help — a bigger pipe with the same oversized buffer bloats just as badly. What fixes it is Smart Queue Management (SQM, sometimes labelled QoS or "bufferbloat mitigation"), configured to just below your real line speed, roughly 85–95%.
Setting it slightly below your line speed moves the bottleneck from your provider's equipment into your own router, where the queue can be managed. You give up a few percent of peak speed and get most of your latency back.
- Check your router first. Many recent consumer models have SQM under a name like "Adaptive QoS", "Airtime Fairness" or simply "bufferbloat". Anything running OpenWrt supports it directly.
- Wi-Fi is its own bottleneck. If you tested over Wi-Fi and got a poor grade, run it again on a cable before you change anything — a congested channel produces exactly the same signature, and no router setting fixes that one.
- Chained routers make it worse. Two devices doing NAT means two queues, and only one of them is yours to configure.
What this test cannot tell you
- Where the bottleneck is. The result says your connection bloats under load. It does not say whether the queue is in your router, your modem, the street cabinet or your provider's uplink. Retesting on a cable, and retesting at a quiet hour, narrows it down more than any single measurement can.
- Anything about your provider's peering. This measures the path to our server. A different destination can behave differently, and a bad grade here is not by itself evidence about a route you have not tested.
- Anything, if your line is very fast. The load is capped at ten seconds and 25 MB per direction, which fills a normal consumer connection for long enough to bloat it — but a 600 Mbit line empties that budget in about a third of a second, which is too few measurements. In that case the page says so and gives no grade.
- Anything, if you are behind a relay. If your connection reaches us through a relay, the test does not run, because it would measure the relay instead of your line.
- Whether the result repeats. Run it a few times across a day before you take it to your provider.
The rest of this site measures the other half of the problem: ping, jitter and packet loss while the line is idle, and how those are measured.
Frequently Asked Questions
What is bufferbloat?
Delay that builds up when your line is busy. Your router or modem holds traffic in a queue instead of dropping it, and every packet, including your game packets, waits behind it. Your speed looks fine; your ping does not.
Why does my ping go up when someone else uses the internet?
Everyone in the household shares one queue. When it fills, your packets wait. A well-configured router keeps the wait to a few milliseconds; a bloated one can add half a second.
How do I fix bufferbloat?
Turn on SQM (sometimes called QoS) in your router and set it to about 85 to 95% of your measured line speed. If your provider box cannot do that, put your own router behind it. A faster plan usually does not help.
Is this a speed test?
No. The throughput figures only show that the load was strong enough. The result is how much your ping rises under load. A gigabit line with a bloated queue scores worse here than a 50 Mbit line with a managed one.
Why can I not run the test on my connection?
Either your connection reaches us through a relay, which the test would measure instead of your line, or UDP is blocked on your network. The page says which of the two applies.
How often can I run it?
Once every five minutes. It fully loads your line for 20 seconds, which disrupts everyone else using it. The normal ping test on the homepage can run for hours.