UFO Test
Pick a speed and watch the UFOs for blur, stutter or trails.
Motion settings
Live readout
- FPS
- --
- Refresh (est.)
- -- Hz
- Pixels per frame
- --
- Late frames
- 0
Frame stats
- Current FPS
- --
- Average FPS
- --
- Min / Max
- -- / --
- 1% low
- --
Shortcuts
- Space pause
- R reset stats
- F fullscreen
This ufo test moves UFOs across the screen at the speed you choose. With three rows, each row runs at half the speed of the one above, so you can compare motion clarity at full, half and quarter speed.
How to run the ufo test
Follow with your eyes
Track one UFO as it moves. Sharp edges mean good motion clarity; a blur or trail means slow pixels or sample-and-hold blur.
Change the speed
Higher pixels per second make blur easier to see. Pixels per frame is the jump between frames.
Go fullscreen
Press F or the Fullscreen button so nothing else moves on screen.
Pixels per second and pixels per frame
Pixels per frame equals speed divided by refresh rate. At 960 px/s a 60 Hz screen moves the UFO 16 px every frame, a 144 Hz screen only 6.7 px, which is why higher refresh rates look smoother.
Frame rate and refresh rate
Frame rate (FPS)
How many new images the browser, game or app produces each second. It depends on your device, the software and how busy the processor and graphics chip are.
Refresh rate (Hz)
How many times per second the screen redraws. It is fixed by the display and its current setting. A browser normally draws once per refresh, so its frame rate tops out at the refresh rate.
What a browser motion test shows
This page measures what your browser actually draws, using requestAnimationFrame. Browsers cap their frame rate at the refresh rate of the display, so the Hz value is an estimate of the rate your screen is running at right now, not the maximum it supports. It cannot measure response time (GtG), input lag, screen tearing or whether the panel itself skips frames; those need special hardware or a camera.
Motion test FAQ
Does it measure response time?
No. It lets you see motion blur and ghosting with your own eyes. Measuring response time in milliseconds needs special equipment.
Why does the UFO jump instead of glide?
Either frames are being dropped (watch the late frames counter) or the speed is high for your refresh rate. Lower the speed or check your display setting.