This UFO test shows the same small craft crossing your screen in three lanes at the same speed. The top lane moves at your screen's full refresh rate, the middle lane at half of it and the bottom lane at a quarter, so on a 144 Hz monitor you compare 144, 72 and 36 frames per second side by side. The readouts show the refresh rate the test measured, how far the craft moves per frame, the blur you should expect and any frames the browser skipped. Run the UFO test on a monitor, laptop, TV or phone in any current browser on Windows, macOS, ChromeOS, Linux, Android and iPhone.
How to run the UFO test
- Let the test run for two seconds. The refresh rate appears and the lane labels change to your real frame rates.
- Keep your eyes on the top craft and follow it across the screen. Then follow the middle and bottom craft and compare.
- Change the Speed to make blur easier to see. 960 pixels per second is the usual speed for comparing monitors.
- Try the Space, Dark, Grey and Light backgrounds. Trails and halos show up differently on each.
- Press Full screen for a bigger view without the page around it. Space pauses, the arrow keys change speed and Esc leaves full screen.
- Check Skipped frames stays at 0 while you judge the motion. A skipped frame makes the craft jump, which is the browser's fault, not the screen's.
Follow the craft with your eyes as it moves, the way you track a target in a game. Staring at one spot while it passes hides most of the blur this test is meant to show.
What the UFO test shows
| Lane or readout | What you should see | What a problem looks like |
|---|---|---|
| Top lane, full frame rate | Smooth, even motion, stripes on the hull readable | Jerky steps, a smeared hull, a dark or bright trail |
| Middle lane, half rate | Visibly steppier than the top lane | Looks the same as the top lane |
| Bottom lane, quarter rate | Clearly jerky, a stutter you can count | Not much worse than the middle lane |
| Pixels per frame | Speed divided by refresh rate, about 7 at 960 px/s and 144 Hz | |
| Expected blur | The smear width a normal screen adds at this speed | Visible blur much wider than this number |
| Skipped frames | 0 | Any number that keeps rising |
The blur readout follows a simple rule. Most LCD and OLED screens hold each frame on screen until the next one, and your eyes keep moving while the picture stands still. That smears the image by the distance the object moves in one frame. At 960 pixels per second the smear is 16 pixels at 60 Hz, 8 pixels at 120 Hz, about 6.7 pixels at 144 Hz and 4 pixels at 240 Hz. This is why a higher refresh rate makes moving things look sharper, not just smoother. The test moves the craft a whole number of pixels each frame so every step is the same size, which can make the speed on screen differ slightly from the button you pressed; the readouts show the real values.
The craft looks blurry
Some blur is normal and the expected blur readout tells you how much. If the craft looks much softer than that, work through these causes:
- The screen runs below its rated refresh rate. Check the reading on the refresh rate test. A 144 Hz monitor left at 60 Hz blurs more than twice as much.
- Slow pixel response. Budget VA panels and older IPS panels change color slowly, which adds a smear on top of the normal blur. Raise the overdrive setting one step, as described below.
- A motion smoothing or noise filter on a TV. Picture modes such as Standard or Vivid add processing. Switch the TV to Game or PC mode.
- Scaling. A monitor fed a resolution below its native one looks soft everywhere. Use the native resolution in your display settings.
To get sharper motion than the refresh rate alone allows, many gaming monitors have a strobing mode that flashes the backlight once per frame: ULMB on NVIDIA G-Sync models, DyAc on BenQ ZOWIE, ELMB on ASUS and Motion Blur Reduction on several other brands. Many OLED TVs offer black frame insertion for the same reason. Strobing cuts blur a lot, but it lowers brightness, can flicker at low refresh rates and often cannot run together with G-Sync or FreeSync.
A trail or halo follows the craft
A dark smear behind the craft on the Grey or Light background is ghosting: the pixels have not finished changing before the next frame. A bright, white or colored edge behind it is overshoot, also called inverse ghosting, which means the overdrive pushes the pixels past their target.
- Open the monitor's on-screen menu and find the overdrive setting. Brands call it Overdrive, Response Time, OD, Trace Free (ASUS) or AMA (BenQ).
- Step through the levels while the test runs at 960 pixels per second. Pick the level with the shortest trail and no bright edge, which is usually the middle setting.
- Check again at the refresh rate you play at. Overdrive tuned for 144 Hz can overshoot at 60 Hz, which is why some monitors look worse when a game's frame rate drops.
The ghosting test puts the craft on dark, grey and light backgrounds at once and adds a ruler that measures the length of the trail.
The motion stutters or jumps
Stutter that you can see while Skipped frames rises comes from the browser, not the monitor. Close other tabs, video calls and games, plug in a laptop, and make sure hardware acceleration is turned on in the browser settings. On a computer with two monitors at different refresh rates, put this window on the faster monitor, and drag it fully onto one screen, not across two.
Stutter with no skipped frames usually means a slow refresh rate. On a 60 Hz screen even the top lane steps 16 pixels at a time at the default speed, which reads as judder. If you are not sure what tearing looks like next to stutter, the screen tearing test shows both.
The top lane looks no smoother than the middle one
The top lane should always look smoother than the half rate lane. If you cannot tell them apart, the screen is probably running at 60 Hz or less, so the top lane shows 60 fps and the middle 30 fps, or you are looking at a TV that adds its own motion processing. Check the lane labels: they show the real frame rates for your screen. If your monitor is sold as 144 Hz but the top label reads 60 fps, the 144hz test page walks through the cable, port and setting problems that cause it.
What the UFO test cannot measure
This is a visual test. It cannot put a number on pixel response time in milliseconds or measure the delay between your mouse and the screen, because a browser never sees the light leaving the panel. Reviewers measure response time with a photodiode and an oscilloscope, and they photograph motion with a camera that slides along with the object. For delay, use the input lag test, and to compare more frame rates at once, such as 30, 60 and 120 fps, use the fps test.
UFO test questions
What is a UFO test?
It is a motion test where a small object crosses the screen in several lanes at the same speed but at different frame rates. Comparing the lanes shows how smooth and sharp your screen makes motion. The name comes from the TestUFO site by Blur Busters, which made this style of test popular. This page uses its own drawings and code.
What should the UFO test look like on a good monitor?
The top craft should glide in even steps, with the yellow canopy and the fine dark stripes on its hull still readable while it moves. The half and quarter lanes should look steppier and blurrier. A dark or bright trail behind the top craft points to slow pixels or too much overdrive.
Why is the UFO test choppy?
Either the browser is skipping frames or the screen runs at a low refresh rate. Check the Skipped frames readout first. If it climbs, close other tabs and apps, plug in your laptop and turn on hardware acceleration. If it stays at 0, check the refresh rate reading: a 60 Hz screen looks choppy next to 120 Hz and above.
Does the UFO test show ghosting?
Yes. Trails behind the top craft are ghosting, and a bright or colored outline is overshoot from overdrive. For a closer look on dark, grey and light backgrounds, with a ruler to measure the trail, use the ghosting test monitor page.
Can I run the UFO test on a phone?
Yes. Phones with 90 or 120 Hz screens show the difference between the lanes clearly. On iPhone, Safari may hold web pages to 60 frames per second, and Low Power Mode does the same, so the top lane can read 60 fps. The refresh rate readout shows what you are getting.
Which speed should I use?
Start at 960 pixels per second, the usual speed for comparing monitors. Faster speeds make blur and trails longer and easier to see. Slower speeds help on small phone screens, where the craft crosses quickly.