Frame pacing test. Smooth, or stutter, as numbers.
A screen can run at the right rate and still stutter, because what matters is whether every frame arrives on time. This times twenty seconds of them, draws each as it lands, and reports four figures with published definitions. There is no composite score.
This check is visual: it draws movement or flicker on the screen, and you judge the result by eye, so a screen reader cannot describe it. The list under "What it measures" says in words what each one shows. If motion or flicker makes you unwell, or you have reduced motion switched on, you can leave it out: no other test on this site depends on it.
One check
- Frame pacing
One check after another, with your progress along the top and a plain verdict on each. Nothing you show the camera or say into the microphone leaves this page.
In short
Frame pacing test: the answer first
A frame pacing test answers whether every frame arrives on time, which is what makes motion feel smooth. It times twenty seconds of frames and reports the late share, hitches, the 99th percentile interval and the 1% low, each with its definition, and no composite score.
Reading your result
- Even, uneven or stuttering
- The verdict comes from the late share and the hitch count with the lines stated on the page, so you can see why it landed where it did.
- The 1% low
- It is the mean of the slowest 1% of frame times, the way games report it. A good average with a poor 1% low is stutter you feel.
- Uneven throughout
- On a laptop, plug in. Turn on hardware acceleration and close overlays and recording tools, then run again.
What it measures
Measured here, not assumed.
- Late share and hitches
- A late frame is over 1.5 times the frame interval, the line TestUFO's skipping test draws. A hitch is 2.5 times or more, counted once and not again as late.
- 99th percentile and 1% low
- The 99th percentile interval in milliseconds, and the 1% low computed the gaming way: the mean of the slowest 1% of frame times, as fps.
- The verdict, our lines
- Even: under 2% late and no hitches. Uneven: 2% or more late, or one hitch. Stuttering: thirty hitches a minute or more, one visible skip every two seconds.
If it fails
The usual failures, and what fixes each.
- Occasional late frames
- Close other tabs and programs, and anything that draws over the screen such as overlays and recording tools.
- Uneven throughout
- On a laptop, plug in: battery power caps the graphics chip. Turn on hardware acceleration in the browser's settings and check the graphics driver.
- Two monitors
- Monitors with different refresh rates can make the browser follow the slower one unevenly. Run with the window on the main monitor.
Where a browser stops
What it cannot tell you.
- It measures the browser's frames, not a game's. A game engine paces its own frames; this shows what the machine and browser can deliver.
- A variable refresh rate panel changes its rate with the content; the browser sees one fixed rate.
- A covered or background tab is slowed by the browser, which would read as stutter and is why the tab must stay in front.
Privacy
Nothing leaves this page.
The camera and microphone are read on this page and stopped as soon as they have been measured. The clip you can play back lives in the browser's memory and is discarded when you leave. The location check discards the position. The internet test sends random bytes to this site and nothing else. The result is stored nowhere unless you ask for it by email, and then only the fact that an email was sent is kept.
Questions
Frame pacing test, answered
- What is frame pacing?
- How evenly frames arrive. Sixty frames a second delivered every 16.7 ms looks smooth; the same sixty with some late and some bunched looks like stutter, at the same average rate.
- Why does my screen stutter at 144 Hz?
- Because frames are missing their refresh. Usually the machine or the browser is busy, a laptop is on battery, or a second monitor at another rate is interfering. The test names late frames and hitches so you can see which.
- Is this the same as input lag?
- No. Input lag is the delay between an action and its result on screen, and a web page cannot measure it. Pacing is whether frames arrive evenly once they are drawn.
- Is frame pacing the same as frame rate?
- No. A screen can run at the right rate and still deliver some frames late. Pacing measures the timing of each frame, not the average.
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