What Is the UFO Test?
The UFO test is a simple motion test made popular by display enthusiasts: a small UFO flies across a dark sky, and you follow it with your eyes. Because the object is simple and moves at a fixed speed, any blur, stutter or judder you see comes from the screen and the frame rate, not from the content.
This online UFO test shows three lanes at once. All three UFOs move at the same speed in pixels per second. The top lane is redrawn on every refresh of your display, the middle lane on every second refresh and the bottom lane on every fourth. On a 144 Hz monitor that means 144, 72 and 36 frames per second side by side, which makes the value of a high refresh rate easy to see without any numbers.
How to Run the UFO Test
- Check the measured refresh rate in the panel. If it shows 60 Hz on a high refresh monitor, fix the system setting first (see the FAQ below).
- Pick a speed. Start at 960 px/s, then try 1920 px/s to exaggerate the difference between lanes.
- Follow one UFO with your eyes for a few seconds, then switch to the next lane. Tracking with your eyes is what makes motion blur visible.
- Enter fullscreen for the cleanest result. Double click the canvas or press ESC to leave.
- Compare settings such as overdrive, motion blur reduction or a different refresh rate, and run the UFO test again after each change.
The UFO test only works well when nothing else is fighting for the GPU. Close video tabs and games, and keep the browser window on the monitor you want to check.
Reading the UFO Test: Smoothness, Blur and Judder
Smoothness
The full-rate lane should glide. The quarter-rate lane visibly steps from position to position. If the top lane also stutters, the browser is dropping frames; close other apps and try again.
Motion blur
When you track a moving UFO, it looks softer than a still one. That is persistence blur from sample-and-hold displays. A common rule of thumb from Blur Busters is that each millisecond a frame stays on screen adds roughly one pixel of blur for every 1,000 pixels per second of motion.
Ghosting and trails
A faint copy behind the UFO is ghosting from slow pixel transitions; a bright or dark outline is often overshoot from aggressive overdrive. The color ghosting test gives a closer look at these trails on different backgrounds.
How Much Blur to Expect at Each Refresh Rate
The table estimates persistence blur on a typical sample-and-hold display at the UFO test's default speed of 960 px/s. Real panels add some blur from pixel response time on top of this.
| Refresh rate | Frame time | Approx. blur at 960 px/s |
|---|---|---|
| 60 Hz | 16.7 ms | about 16 px |
| 120 Hz | 8.3 ms | about 8 px |
| 144 Hz | 6.9 ms | about 7 px |
| 240 Hz | 4.2 ms | about 4 px |
That is why the jump from 60 Hz to 144 Hz is so obvious in the UFO test, while the step from 144 Hz to 240 Hz is smaller but still visible at high speeds. For background on refresh rates in general, see the refresh rate article on Wikipedia.
UFO Test Problems and Fixes
- Stuck at 60 Hz: set the refresh rate in Windows Display settings or macOS Displays, use DisplayPort or a high-bandwidth HDMI cable, and disable battery saver on laptops.
- Regular stutter in the top lane: another app may be using the GPU, or the browser has hardware acceleration turned off.
- Tearing lines: visible horizontal breaks usually point to VSync being off at the system level. Browsers normally sync to the display, so tearing here is uncommon.
- Different results on two monitors: browsers often follow the refresh rate of the primary display. Move the window and reload the UFO test.
To confirm the number itself, the screen Hz test shows a live refresh rate readout with history.
Why Use This UFO Test
- Automatic lanes: the UFO test measures your refresh rate and sets the half and quarter lanes from it.
- Four speeds from 240 to 1920 px/s for gentle or extreme motion.
- Sharp on high-DPI screens: the canvas renders at your device pixel ratio.
- Private and free: the UFO test runs locally in your browser with no sign-up.
- Next step: compare any frame rates you like, such as 30 vs 60 vs 144, in the FPS test.
UFO Test FAQ
What does the UFO test show?
The UFO test moves the same object across the screen at the same speed in three lanes. The top lane updates on every refresh, the middle lane at half that rate and the bottom lane at a quarter. The difference in smoothness and blur between the lanes shows what your refresh rate does to motion.
Why does my UFO test say 60 Hz on a 144 Hz monitor?
The browser can only animate as fast as the operating system runs the display. Check that Windows or macOS is set to 144 Hz, that the cable and port support it, and that the browser is on the high refresh monitor. Laptops on battery saver and some remote desktop sessions also limit the rate to 60 Hz.
Why is the UFO blurry even at a high refresh rate?
Most LCD and OLED screens are sample-and-hold displays: each frame stays lit until the next one. As your eyes track the UFO, the held frame smears across the retina. Higher refresh rates shorten each frame and reduce that blur, but only strobing backlights or black frame insertion remove most of it.
Which UFO test speed should I use?
960 pixels per second is a good default. Use 480 px/s to look at fine detail and 1920 px/s to exaggerate motion blur and stutter. Faster speeds make the gap between 60 Hz and 144 Hz much easier to see.
Does the UFO test measure response time?
No. The UFO test is a visual comparison. It shows blur and smoothness as your eyes see them but does not measure pixel response time in milliseconds. For trails and overshoot on colored objects, try the color ghosting test.
Can I run the UFO test on a phone?
Yes. The UFO test works in mobile browsers. Many phones with 90 Hz or 120 Hz screens lower the rate in power-saving mode, so turn that off and set the display to its highest refresh option before testing.