Bufferbloat Test
Measures your ping while idle, then while your connection is busy downloading and uploading. The difference is bufferbloat: the hidden cause of lag when someone else is streaming.
1Idle
– ms
Baseline ping
2Downloading
– ms
– ms– Mbps
3Uploading
– ms
– ms– Mbps
Bufferbloat grade
What is bufferbloat?
Routers hold packets in a queue (a buffer) when the line is busy. If that queue is too big, a large download fills it and every other packet, including your game or call, has to wait in line behind it. Your speed looks fine, but ping jumps from 20 ms to 200 ms or more the moment someone starts a download or a backup.
That’s why a normal speed test can look great while video calls still freeze. This test catches it by measuring ping while the connection is full.
How the grade works
| Grade | Extra latency under load | What you’ll notice |
|---|---|---|
| A+ | Under 5 ms | Nothing. Gaming and calls stay smooth while others stream. |
| A | 5–30 ms | Very little. |
| B | 30–60 ms | Slight delay in fast games during big downloads. |
| C | 60–200 ms | Calls stutter and games lag when the line is busy. |
| D | 200–400 ms | Web pages stall during uploads; calls break up. |
| F | Over 400 ms | The connection feels broken whenever it’s busy. |
The grade uses the worse of the two loaded results. Upload bufferbloat is the most common, because upload is the narrower pipe on most plans.
How to fix bufferbloat
- Turn on SQM or Smart Queue Management. Many routers have it, sometimes called “QoS”, “Adaptive QoS” or “Smart Queue”. It keeps the queue short. Set it to about 90% of your measured speeds.
- Pause heavy uploads. Cloud photo backup is the classic culprit.
- Upgrade old router firmware, or use a router that supports modern queue management (fq_codel or CAKE).
Read the full walk-through in what is bufferbloat and how to fix it, or check your idle latency first with the ping test.