Frame pacing test: find stutter and 1% lows
A high average frame rate can still feel rough if frames arrive unevenly. This test records the time of every frame as a square moves, then shows average fps, the 1% low and how many frames were late.
Why frame pacing matters more than average fps
Average frame rate hides stutter. Two systems can both show 100 frames per second on average, yet one delivers a frame every ten milliseconds and the other alternates between five and fifteen. The second feels rough because your eyes notice the uneven rhythm, not the average. That is why reviewers publish the one percent low figure, which describes the slowest frames and so tracks what you feel.
This test measures the time between every frame the browser draws while a square moves smoothly across a lane. It reports the median frame time, the 99th percentile frame time and the matching 1% low fps, plus how many frames arrived late, which means more than one and a half times the median.
Frame time and what it feels like
Typical ranges for steady frame times and how they feel. Smoothness depends on consistency as much as the number.
| Steady frame time | Frame rate | Feel |
|---|---|---|
| 33.3 ms | 30 fps | Playable but choppy |
| 16.7 ms | 60 fps | Smooth |
| 8.3 ms | 120 fps | Very smooth |
| 6.9 ms | 144 fps | Very smooth, low latency |
| 4.2 ms | 240 fps | Extremely smooth |
How to read the results
A smooth result has a 99th percentile close to the median, almost no late frames and a worst frame under about double the median. A few late frames over a long run are normal. Many of them, or a worst frame many times the median, point to something stealing time: a background app, power saving, an overheating processor, a driver problem or a display running in a mode that does not match the animation.
The spread table groups frames by how far they were from the median. Most should sit in the first row. If lots appear in the lower rows, close other programs, switch to the high performance power plan and run again. Compare with a clean run after restarting the computer to see how much background load matters.
From browser test to game stutter
The test cannot replace a game benchmark, since a game puts different load on the graphics card, the processor and the memory. But the same causes of stutter often appear here as well: slow background tasks, thermal throttling and poor power settings. If this test is clean and a game still stutters, the cause is likely in the game, such as shader compilation or streaming from a slow drive.
Use the 1% low fps calculator to work out lows from your own capture data, the FPS to frame time converter to translate between the two, and the refresh rate checker to confirm what your display is doing.
How to use the frame pacing test
- Choose the test length. Five seconds is enough for a first look.
- Keep this tab in front and press Start test.
- Watch the square and avoid using the computer.
- Read the average fps, 1% low and late frame count.
- Fix background load or power settings, then run it again to compare.
Common mistakes to avoid
- Judging by average fps alone and ignoring the 1% low.
- Running the test while downloads or updates run in the background.
- Comparing one run on a laptop on battery with another on mains power.
Related tools and guides
Keep going with these: Refresh rate checker, 1% low FPS calculator, FPS to frame time converter, Response time vs refresh rate calculator, does frame generation add input lag.
Frequently asked questions
What is frame pacing?
Frame pacing is how evenly frames are delivered over time. Perfect pacing delivers each frame after the same gap. Uneven pacing causes stutter even when the average fps looks high, because the rhythm of the picture is irregular and your eyes notice the difference.
What is 1% low fps?
It is the frame rate of the slowest one percent of frames, usually calculated from the 99th percentile frame time. It describes the worst moments, so it tracks stutter far better than the average does. A small gap between average and 1% low means smooth play.
Why does my screen stutter in the test?
Common causes are background apps, power saving, thermal throttling, a busy drive or a driver problem. Close extra programs, use the high performance power plan, plug a laptop into power and run again. If it improves, a background task was the cause.
Does this test measure game performance?
No. It measures how evenly your browser draws frames, which reflects the display, drivers and system load. Games stress the graphics card and processor differently, so use a game benchmark for fps and use this test to spot general stutter causes.
How long should I run the test?
Five seconds gives a quick check and ten to twenty seconds gives a steadier 1% low figure, because more frames mean a better sample of the slow ones. Run it twice, and compare runs at the same time of day and power setting.
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