Lag test (bufferbloat)
Find out why games and video calls lag when someone streams or uploads. Measure your lag under load, get a grade, and learn how to fix it.
Takes about 25 seconds and uses up to about 85 MB of data, so on mobile data you may prefer Wi-Fi.
Your connection can be fast and still feel slow. When someone streams, uploads photos or backs up files, routers often let data pile up in a queue, and everything else waits behind it. That waiting is called bufferbloat, and it's why games stutter and video calls freeze at the busiest moments.
How the test works
It measures your response time at rest, then again while your connection is busy downloading and then uploading. The difference is the lag that busy traffic adds. The busy traffic travels on separate connections, so the measurements don't wait behind it.
Grades
- A+ or A (under 30 ms extra): great for gaming and video calls.
- B (30 to 60 ms extra): fine for most uses.
- C (60 to 200 ms extra): you'll notice lag in games and calls when the connection is busy.
- D or F (200 ms or more extra): serious lag whenever anyone uses the connection heavily.
How to fix bufferbloat
- Turn on smart queue management in your router, if it has it. Look for names like SQM, Smart Queue, Adaptive QoS, or fq_codel or CAKE. Setting it slightly below your plan's speed usually helps most.
- Pause big uploads such as cloud photo backups and file syncing during games and calls. Uploads cause the worst lag on many connections.
- Use a cable for the console or PC that matters most.
- Consider a newer router if yours has no queue management. The modem from your provider often has none.
Limits
To save your data, the test stops after about 60 MB down and 24 MB up. On very fast connections that may not fill the line, so the grade can look better than reality. Results also change with whatever else your network is doing, so run it a few times. Want a fuller picture? Fix my internet tests your whole connection.
Last updated October 2026.