Bufferbloat Test
Measure how much your latency spikes under load — the hidden lag that ruins gaming and calls the moment your line gets busy.
Bufferbloat test
Measures your latency while idle, then again while a download saturates your line. The gap is your bufferbloat.
Idle — press “Run bufferbloat test”. This sends a sizeable download, so it uses some data.
What this test measures
Bufferbloat is the single biggest reason a “fast” connection feels terrible for gaming and calls. When your router or modem has oversized buffers, it queues packets instead of dropping them the moment the line gets busy — so your latency, which looks great at rest, suddenly jumps by hundreds of milliseconds during any download or upload. This test captures that effect directly: it records your idle latency, then floods the line with a sustained download while continuing to ping, recording your latency under load. The difference is graded from A+ (flat under load) to F (severe bloat).
How to read your result
| Latency increase | Grade | Meaning |
|---|---|---|
| < 5 ms | A+ / A | Latency stays flat under load |
| 5–30 ms | B | Minor, rarely noticeable |
| 30–100 ms | C / D | Calls and games suffer when busy |
| > 100 ms | F | Severe — everything stalls under load |
A poor grade is good news in one way: bufferbloat is fixable. Smart Queue Management (SQM, also called fq_codel or CAKE) on your router keeps latency flat under load. Before you change hardware, confirm the baseline with the ping test and check stability over time with the long-run stability test.
Some product recommendations on speedtest.doctor are affiliate links — we may earn a commission, at no extra cost to you. We only suggest gear that addresses the measured problem.
Frequently asked questions
- What is bufferbloat?
- Bufferbloat is latency that spikes when your connection gets busy. Oversized buffers in routers and modems hold data instead of dropping it, so the moment a download or upload starts, your ping balloons — and games, calls and video conferencing fall apart even though your speed test looks great.
- How does this test measure it?
- First we measure your idle latency. Then we start a sustained download and keep pinging while the line is fully loaded. The difference between loaded and idle latency is your bufferbloat. A big jump means your equipment is buffering badly.
- How do I fix bufferbloat?
- The proven fix is Smart Queue Management (SQM/fq_codel/CAKE) on your router. Many modern and gaming routers support it, as does OpenWrt. Capping your speeds slightly below your line's maximum in the SQM settings keeps latency flat under load.
- Why does my ping look fine but games still lag when others use the internet?
- That's classic bufferbloat. Your idle ping is low, but as soon as someone streams or uploads, latency spikes for everyone. This test reproduces that condition deliberately so you can see it instead of guessing.
Bad bufferbloat? Here's the cure
The Doctor reads your bufferbloat grade alongside ping, jitter and throughput, then gives you a prioritised fix list — from a free SQM setting to the right router for your line.