How to use
- Put the browser window on the screen you want to test and keep this tab in front.
- Wait a second or two. The measured refresh rate appears at the top, with average FPS, frame time, jitter and dropped frames below.
- Follow the moving block in the motion blur test with your eyes. Switch speeds to compare how sharp it looks.
Options explained
- Refresh rate (Hz)
- Worked out from the median interval of the last 120 frames (two seconds at 60 Hz, less on faster screens). Values within 3% of a common rate such as 60, 120, 144, 165 or 240 Hz are shown as that rate.
- Jitter
- The standard deviation of frame intervals. Smaller is steadier; it is normally under 1 ms.
- Dropped frames
- When a frame takes more than 1.5 times the expected interval, the missed frames are counted. Background programs and a busy browser both cause them.
How the numbers are worked out
The page records the time between consecutive animation frames and uses the latest 120 of them, with a minimum of 10. The refresh rate is 1000 divided by the median interval in milliseconds, snapped to a common rate when it is within 3% of one of these: 24, 30, 48, 50, 60, 72, 75, 90, 100, 120, 144, 165, 170, 180, 240 or 360 Hz.
| Refresh rate | Expected frame time |
|---|---|
| 60 Hz | 16.7 ms |
| 75 Hz | 13.3 ms |
| 90 Hz | 11.1 ms |
| 120 Hz | 8.3 ms |
| 144 Hz | 6.9 ms |
| 165 Hz | 6.1 ms |
| 240 Hz | 4.2 ms |
A frame counts as late when its interval is more than 1.5 times the median. Each late frame adds its interval divided by the median, rounded, minus one to Dropped frames. At 60 Hz, a 20 ms interval adds nothing, a 33 ms interval adds 1 and a 50 ms interval adds 2. In the frame-time graph, each bar is one of the last 240 frames, late frames are drawn in a warning colour, and the line marks the expected frame time.
In the motion blur test the block moves at 480, 960 or 1920 pixels per second for Slow, Medium and Fast. Numbers on the page update twice a second.
Frequently asked questions
My monitor is 144 Hz. Why does it show 60 Hz?
First check the refresh rate in your display settings (Windows - Settings → System → Display → Advanced display; macOS - System Settings → Displays). Then check the cable and port, as some HDMI cables and ports only carry 60 Hz. Laptops on battery may also be limited by power saving.
Why do Mac and iPhone ProMotion screens show 60 Hz?
Safari limits page animation to about 60 Hz by default to save power. On a Mac you can test in Chrome, or turn off "Prefer Page Rendering Updates near 60fps" in Safari's Feature Flags. Low Power Mode on an iPhone also caps it at 60 Hz.
How is this different from the refresh rate on the screen resolution page?
The resolution page samples for about one second when it opens, as a quick reference. This test keeps measuring and shows the frame-time graph, jitter and dropped frames, so you can check high refresh is stable.
How accurate is it?
It measures the frame rate the browser actually renders, which normally matches the display's current refresh rate. A much lower result usually means high refresh is not turned on, power saving is limiting it, or the computer is very busy.
Privacy
This tool runs entirely in your browser. Your files and text are processed on your device and are never uploaded to our servers.