How to Test Monitor Refresh Rate & Frame Drops
Verify true operating refresh rate, detect 60Hz lockouts, and inspect frame pacing in your browser.
1. How Browsers Measure Refresh Rate
Web browsers utilize the high-resolution `requestAnimationFrame` (rAF) API synced to the operating system display compositor. By recording timestamps over hundreds of consecutive VSync cycles, ScreenCheck calculates the exact interval between displayed frames.
At 60Hz, the interval is exactly 16.67 milliseconds.
At 120Hz, the interval is 8.33 milliseconds.
At 144Hz, the interval is 6.94 milliseconds.
At 240Hz, the interval is 4.17 milliseconds.
Browser measurement vs. Physical Hardware: The browser observes the software presentation cadence of the window compositor. It cannot physically probe the display panel timing controller (TCON).
2. Why Your Monitor Might Be Stuck at 60Hz
Many users purchase 144Hz or 240Hz monitors but unwittingly run them at 60Hz for months due to operating system defaults or incorrect cables.
• Windows: Right-click desktop → Display settings → Advanced display → Choose a refresh rate.
• macOS: System Settings → Displays → Refresh Rate dropdown (ensure ProMotion or high Hz is selected).
• Cable Bandwidth: Older HDMI 1.4 cables cannot carry 144Hz at 1440p or 4K. Use DisplayPort 1.4 or HDMI 2.1.
• Multi-Monitor Mismatch: Having a 60Hz secondary display can occasionally cause Windows DWM or GPU drivers to throttle browser animation to 60Hz when video plays on the second screen.
3. Testing for Frame Skipping
Some monitors claim high refresh rates (or overclocked modes) but secretly drop frames because their internal scalers cannot keep up. This results in stutter despite the OS reporting 144Hz.
To test for frame skipping: Launch the ScreenCheck Frame Drop Test with moving blocks, take a high-shutter-speed photograph of your screen with a smartphone (shutter speed ~1/10 to 1/20s). If every block is lit consecutively without gaps, your panel displays all frames without skipping.
Recommended Interactive Tests
Run these dedicated fullscreen tools to test your display against this guide's criteria:
Frequently Asked Questions
Why does the test show 59.94Hz instead of 60Hz?
59.94Hz is the standard NTSC broadcasting timing frequency. It is completely normal and indistinguishable from 60.00Hz.
Can hardware acceleration affect refresh rate?
Yes! If "Hardware Acceleration" is disabled in your browser settings, animations render on the CPU and will often stutter or lock to 60Hz.
Related Diagnostic Guides
Continue learning with complementary display inspection guides:
60Hz vs 120Hz vs 144Hz vs 240Hz: What Really Matters?
Compare 60Hz, 120Hz, 144Hz, and 240Hz frame times, understand how persistence blur decreases with refresh rate, and see visual comparisons.
What is VRR? G-Sync, FreeSync & Variable Refresh Explained
Learn how Variable Refresh Rate (VRR) synchronizes your monitor refresh rate dynamically with your GPU frame output, eliminating tearing and stutter.