Bufferbloat test
Measures your idle ping, then keeps measuring while short download and upload bursts fill your line. The grade shows how much latency your router adds when the connection is busy.
"Test under load" adds short download and upload bursts to show bufferbloat.
Latency trace
Teal is idle, amber is under load, red marks a packet with no reply.
Distribution
How often each round-trip time occurred.
The distribution appears after the first test.
Diagnostics from Chicago (US)
These tests run from our test node in Chicago (US), not from your browser. Use them to check whether a host is reachable and how far it is from a US Midwest network. Private and internal addresses can't be tested.
What bufferbloat is
Routers and modems hold packets in a queue when more data arrives than the line can send. If that queue is too large, packets wait in it for a long time, so a video call or game stalls whenever someone starts a download or a backup runs. The connection is not slow; it is laggy only when busy.
Idle speed tests miss this completely, which is why bufferbloat is so common and so rarely diagnosed.
How the grade works
The test compares the median ping during the download and upload bursts with the idle median. An increase under 5 ms earns an A+, under 30 ms an A, under 60 ms a B, under 200 ms a C, under 400 ms a D, and anything more an F. The latency trace marks loaded samples in amber so you can see exactly when ping climbed.
The bursts are short and capped, so the test uses little data, but on a slow upload line the upload phase can still take several seconds.
How to fix bufferbloat
- Turn on SQM (Smart Queue Management) in your router. Look for "Smart Queue", "QoS", "fq_codel" or "CAKE" in the settings.
- Set the SQM limits to about 90% of your measured download and upload speeds.
- If your router has no SQM, routers running OpenWrt, or many recent gaming and mesh routers, include it.
- Run the test again: a working setup usually moves the grade to A or B.
Questions
How do I test for bufferbloat?
Press "Start bufferbloat test". It measures idle ping, then measures again during short download and upload bursts, and grades the difference.
Why am I suddenly getting bufferbloat?
Usually because something started using the line: a backup, game update, or another person streaming. It can also appear after a speed upgrade if your router SQM limits were set for the old speed.
Is bufferbloat a real problem?
Yes. It is one of the most common causes of lag in calls and games on connections that otherwise test fast.
Does a faster plan fix bufferbloat?
Not reliably. A faster line fills up less often, but when it does fill, an oversized buffer still adds the same delay. SQM fixes the cause.