Refresh Rate, Frame Pacing & Variable Refresh Rate (VRR)
How panel refresh cycles, GPU frame delivery, and browser animation timing interact.
Refresh rate (measured in Hertz, Hz) is how many times per second your monitor draws a new image, while frame rate (FPS) is the speed at which your graphics card generates frames.
Why It Matters
If your monitor is set to a lower refresh rate than it supports (such as running a 144Hz gaming display at default 60Hz), you lose motion fluidity, increase perceived input lag, and fail to benefit from your display hardware.
What Users Should Look For
- Choppy mouse cursor motion when sweeping across the desktop
- Stutter or frame skipping during fast scrolling or high-speed gaming
- Mismatch between advertised monitor refresh rate (e.g., 144Hz) and browser-observed frame timing
- Screen tearing when frame delivery is unsynchronized with the display scanout
How to Test This Parameter
- 1Run the Refresh Rate Test in Screen Tester to observe real-time `requestAnimationFrame` render intervals
- 2Inspect the frame pacing histogram for jitter, dropped animation frames, or micro-stutters
- 3Run the VRR Visual Inspection test under dynamic motion workloads to inspect tearlines and frame cadence
Technical Testing Boundaries & Methodology
Screen Tester emphasizes transparency: we clearly delineate between what web browser engines can mathematically inspect versus what requires specialized physical laboratory probes.
- ✓Timestamp intervals between successive browser rendering cycles via `requestAnimationFrame`
- ✓Estimated active display refresh rate derived from mathematical frame delta statistical averaging
- ✓Frame pacing consistency (jitter standard deviation, dropped frame counts during animation loops)
- ✕Hardware panel G-Sync module state or VESA Adaptive-Sync handshake protocol over DisplayPort/HDMI
- ✕Hardware backlight strobe frequency (ULMB, DyAc, or ELMB black frame insertion)
- ✕Physical pixel liquid crystal rise/fall response times (GtG transition milliseconds)
Hz vs. FPS: The Crucial Difference
Refresh rate (Hz) is a fixed physical cycle of the display hardware: a 120Hz panel refreshes its scanout lines every 8.33 milliseconds, regardless of whether the source image changed.
Frame rate (FPS) is variable: it reflects the computational speed of the graphics pipeline rendering completed image frames to the front frame buffer.
When FPS exceeds Hz or falls out of synchronization, screen tearing occurs. When FPS drops below Hz without VRR, duplicate frames produce motion stutter and judder.
Browser requestAnimationFrame Mechanics
Web browsers align animation loops with the monitor vertical blanking interval using the `requestAnimationFrame` API. On properly configured high-refresh systems, browsers fire callbacks at 120Hz, 144Hz, or 240Hz.
However, browsers will throttle frame rates to 60 FPS if running on battery power, if background video playback dictates a 30/60 FPS cadence, or if hardware acceleration is unavailable.
Common Causes
- •Operating system display settings left at default 60Hz after connecting a high-refresh monitor
- •Using an older HDMI 1.4 or uncertified video cable that lacks bandwidth for high refresh rates at native resolution
- •Browser hardware acceleration disabled, forcing software CPU composition capped at 60 FPS
- •Secondary low-refresh display (e.g., 60Hz screen alongside 144Hz) forcing browser compositor downclocking
Recommended Next Steps
- →Open Windows Display Settings > Advanced Display and verify the Refresh Rate dropdown is set to maximum
- →Ensure your GPU control panel (NVIDIA Control Panel or AMD Software) has G-Sync/FreeSync enabled
- →Verify your video cable is DisplayPort 1.4 or HDMI 2.1 capable of full native bandwidth
Frequently Asked Questions
Why does my 144Hz monitor only show 60Hz in the test?
The most common cause is that Windows or macOS has not been configured to output 144Hz. Open your OS display settings to verify the output refresh rate, and ensure hardware acceleration is toggled ON in your browser settings.
Can a browser test prove that G-Sync is actively working?
No web application can read internal GPU hardware registers to certify G-Sync engagement. Screen Tester provides visual pendulum patterns to observe whether tearing and judder are absent.