What Is Bufferbloat and How Do You Fix It?

The problem in plain words

Your connection can feel perfectly fast, and still stutter whenever someone uploads a photo or starts a download. Video calls freeze, games lag, and web pages stall. A common cause is bufferbloat.

What bufferbloat is

Routers and modems have buffers, which are small waiting areas for data that cannot be sent immediately. When a buffer is too large, it fills up during a big transfer. Your small, urgent packets, such as the ones for a call or a game, then wait in a long line behind the big ones. The result is a sharp rise in latency while the line is busy, even though your speed is unchanged.

How to spot it

1. Note your normal ping. The speed test shows it as "Ping".
2. Look at the latency under load figure in the results. It is your ping measured while data is moving.
3. Compare them. If latency under load is only a little higher than your idle ping, you are in good shape. If it jumps by a hundred milliseconds or more, you probably have bufferbloat.

The test estimates this from your browser, so run it a few times to see the pattern. You can also test by hand: start a large download or upload, and run ping 1.1.1.1 in a command window at the same time. If the ping times climb, that is bufferbloat.

Why it matters

• Video calls freeze or get robotic when someone else uses the connection.
• Online games lag at the worst moments, usually when something else is uploading.
• Browsing feels slow during downloads, even when the download speed looks fine.

How to fix it

1. Enable smart queue management (SQM) on your router. Many modern routers offer settings with names such as SQM, Smart Queue, fq_codel or CAKE. They manage the queue so that small packets are not stuck behind big ones.
2. Set the limits just below your real speeds. Run the test on a cable, then enter download and upload limits of about 85 to 95 percent of the measured values. This keeps the queue in your router, where it can be managed, and not in the modem or provider's equipment.
3. Use the quality-of-service (QoS) setting your router offers, and prioritize calls and games if it lets you choose.
4. Use a cable for important devices. This does not fix bufferbloat, but it removes Wi-Fi delays on top of it.
5. Check for firmware updates, because some routers add or improve queue management in updates.
6. Consider a different router if yours has no queue-management options at all.
7. Ask your provider whether their equipment has a setting for it, or whether they can offer a better modem.

After any change, test again and compare the latency-under-load figure.

What not to expect

Fixing bufferbloat does not raise your speed. It makes the connection feel steadier and more responsive. If your speeds are also below your plan, read are you getting the speed you pay for?.

Related reading

Ping, jitter and packet loss explained explains the numbers used here. Why is my Wi-Fi slow? covers the other common causes of a laggy connection.