This test measures the rate reaching this browser window on the display where the window is rendered. It is useful for checking whether the browser result lines up with the refresh rate you selected, but it does not read the monitor model, cable, port, panel maximum or game FPS.
How to Read the Result
The result panel shows both an interpreted rate and supporting timing details. A normal run usually finishes after a few seconds once enough usable browser-frame samples have been collected.
Large Hz number
When the measured timing is close to a familiar standard rate, the large number uses that standard value. If the timing does not closely match a standard rate, the interface uses a rounded version of the raw result.
Raw Hz
The raw value comes from the median interval between browser animation frames after the warmup period. Values such as 59.9, 119.8 or 143.8 are normal raw timing results.
Confidence
Confidence reflects whether the run collected enough uninterrupted samples, whether the frame timing stayed reasonably consistent and whether the tab stayed visible and focused.
Pacing and jitter
Pacing describes how consistent the browser frame intervals were during that run. Uneven pacing or low confidence means you should run the test again before drawing hardware conclusions.
Drops and interruptions
Drops mean some browser-frame intervals were much longer than the normal rhythm for that run. They do not automatically identify a cable problem, GPU fault, monitor defect or panel issue.
What it is not
These fields describe browser-session timing. They are not a direct panel response-time, ghosting or hardware-health test.
Compare It With the Refresh Rate You Selected
Judge the result against the refresh rate selected in your operating-system display settings. The same measured number can be normal or wrong depending on what you intended to run.
Matches the selected rate
Example: you selected 144Hz, the raw result is near 144 and the interpreted result shows 144Hz. That broadly matches the current browser result for this window on this display.
Slightly below or above
Examples: 59.9 instead of 60, 119.8 instead of 120 or 143.8 instead of 144. Small raw timing differences are normal; the familiar interpreted rate is shown separately.
Appears capped near 60Hz
This is only a problem when you expected a higher refresh rate. If you selected 120Hz, 144Hz, 165Hz or higher and the browser stays near 60Hz, use the troubleshooting path below.
Stable intermediate rate
Example: you expected 240Hz, but the result is stable around 144Hz. That is not the same as a 60Hz cap or an unstable run. First check the OS-selected refresh rate and resolution, then review the display mode, dock, adapter, output path and browser delivery.
Unstable result
Large swings, low confidence, interruptions or high pacing variation should be tested again. A steady 60Hz result is a cap question. A result moving widely between 80Hz and 165Hz is first a test-condition or browser-delivery question.
Why It Shows 60Hz When You Expected More
Start with the branch that matches your operating-system display settings. Change one meaningful condition at a time, then run the test again under the same window placement.
The operating system only offers 60Hz
If the operating system does not offer the higher mode, focus on the selected display mode and the physical display path before blaming the browser.
Select the correct display
In display settings, confirm you are adjusting the monitor you meant to test.
Confirm resolution and refresh rate
Some higher refresh modes appear only at certain resolutions or display modes.
Check the monitor on-screen menu
Some monitors require a high-refresh, performance or overclock mode before every option appears in the OS.
Use the intended graphics output
On a desktop with a dedicated GPU, confirm the display is connected to the GPU output rather than an unintended motherboard output.
Review the complete output path
Check the GPU or computer output, dock or adapter, cable and monitor input. The test can narrow the problem to the display path, but it cannot identify which physical component is imposing the limit.
Check mirrored displays
Duplicated or mirrored displays can force screens with different capabilities into a shared lower mode.
Update the graphics driver when appropriate
If the expected mode is missing, install or reinstall the driver from the GPU or computer maker, then reopen display settings.
Run the test again
After one change, place the browser window on the same display and compare the result again.
The operating system is set higher, but the browser remains near 60Hz
If the OS already shows the higher rate, focus on browser delivery conditions. Fullscreen can reduce distractions and make display placement clearer, but it is not required for the measurement itself.
Place the window fully on the display being tested
A window partly across two displays can be rendered under the wrong cadence.
Keep the tab visible and focused
Hidden, background or blurred tabs can pause or invalidate browser animation timing.
Restart the browser after changing OS refresh rate
If the browser still reports the old rate, close and reopen it before changing hardware.
Check battery or power-saving modes
Laptops and high-refresh mobile devices may reduce delivered refresh behavior to save power.
Check browser hardware acceleration
If hardware acceleration is disabled, enable it and run the test again.
Use the normal browser
Retest in Safari, Chrome, Edge or Firefox directly rather than inside an in-app browser, embedded web view or saved web app.
Apply Safari guidance only where relevant
Safari and WebKit behavior varies by OS and browser version; see the Apple-specific section below before changing experimental settings.
Run the test again after each meaningful change
Keep the same display, window placement and power state when comparing results.
The browser result is correct, but a game or app remains at 60 FPS
If this browser window reaches the refresh rate you selected, the display/browser path appears to be running at that measured rate. A remaining 60 FPS limit is likely app-specific, such as a game frame cap, display mode, graphics setting or synchronization configuration. This page does not measure or troubleshoot in-game FPS in depth.
Why the Number Is Slightly Off or Keeps Moving
Use these cases to decide whether to accept the result, clean up the test conditions or investigate a setting change.
143.8Hz instead of 144Hz
Treat this as normal raw browser timing when the interpreted result is 144Hz and confidence is reasonable.
59.9Hz instead of 60Hz
A raw value just under 60Hz is usually an ordinary timing result, especially when 60Hz is the selected mode.
Low confidence
Run the test again with the tab focused, the window fully on the target display and fewer heavy tasks running.
Uneven pacing
Uneven browser-frame intervals can make motion feel inconsistent during that run. Test again before changing cables, ports or monitor settings.
Interrupted run
If the tab lost focus, the page was hidden or the browser hit a long pause, treat the result as a bad run and repeat it.
Result changes between monitors
Different displays can run different refresh modes. Move the window fully onto the monitor you want to check and run the test there.
Result changes on battery power
Power-saving behavior can affect high-refresh delivery on laptops and mobile devices. Plug in, disable the saver if appropriate and compare again.
What This Result Can and Cannot Tell You
The number is the last stage in this chain: Display capability -> selected operating-system mode -> browser delivery -> ScreenDetect result. A display may support one maximum rate, the operating system may currently select another and the browser may deliver another cadence to this window.
Use this result for
Measure the effective cadence reaching this browser window
Compare the result with the rate you selected or expected
Identify a likely near-60 cap when you expected a higher rate
Separate a stable low result from an unstable run
Compare results after a display, power or settings change
The result does not identify
The panel's advertised maximum
The exact cable, dock, adapter or physical port
EDID details
FreeSync or G-Sync support
GtG or MPRT response time
In-game FPS
Monitor overclock stability
Which physical component is limiting the mode
Refresh Rate Is Not the Same as Game FPS
Safari, Multiple Monitors and Laptop Power
Safari and high-refresh Apple devices
Safari and WebKit behavior can vary by operating-system and browser version. On supported devices, first turn off Low Power Mode, confirm the selected display refresh rate and run the test in Safari itself rather than an in-app browser or saved web app. Some Safari versions expose page-rendering preferences in Feature Flags, but the name and availability can change.
Apple documentation supports the Low Power Mode and display refresh-rate checks. WebKit issue history supports treating Safari page-rendering flags as version-dependent browser behavior, not as a stable Apple Support step.
Multiple monitors
The result reflects the display where this window is being rendered. Place the window fully on the target display before testing. Moving the window between a 60Hz laptop panel and a 165Hz external monitor can change the result, and the tool does not identify the physical monitor model.
Laptop power and external displays
Battery-saving behavior, docks, hybrid graphics and external-display routing may affect which refresh modes are available or delivered. Keep this section as a clue, then use the OS-only-60 or browser-near-60 branch above for the actual checks.
When the Problem Is Not Refresh Rate
Next diagnostic routes
If the Hz result matches the selected rate but the screen still looks wrong, use the test that matches the visible symptom.
Sources
- Window: requestAnimationFrame() · MDN Web DocsDirect support for browser animation callbacks generally matching display refresh rate and pausing in background or hidden tabs.
- Change the refresh rate on your monitor in Windows · Microsoft SupportDirect support for checking the selected display, current resolution, current refresh rate and available Windows refresh-rate choices.
- Use Low Power Mode to save battery life on your iPhone or iPad · Apple SupportDirect support for Low Power Mode reducing display refresh rate on iPhone and iPad models with ProMotion display.
- Change the refresh rate on your MacBook Pro or Apple display · Apple SupportDirect support for checking and changing refresh rate on supported MacBook Pro and Apple displays.
- 'Prefer Page Rendering Updates near 60fps' is no longer available in the Experimental Features menu · WebKit BugzillaBrowser-engine evidence that Safari page-rendering feature flags are version-dependent and should not be presented as stable Apple Support guidance.
- Full Text Bug Listing: requestAnimationFrame rates above 60fps · WebKit BugzillaBrowser-engine issue history for high-refresh requestAnimationFrame behavior in WebKit/Safari.
- ScreenDetect Refresh Rate Test implementation · ScreenDetectScreenDetect tool behavior verified from the current implementation: browser frame timing after warmup, interpreted standard-rate display, confidence labels and pacing output.
Refresh Rate Test FAQ
Why does the test show 143.8Hz instead of 144Hz?
Raw browser timing often lands slightly below or above the label selected in your operating system. If the interpreted result shows 144Hz and the run has reasonable confidence, a raw value like 143.8Hz is normally close enough to treat as a match.
How accurate is a browser refresh rate test?
It is usually accurate enough to check common display modes when the tab stays visible, focused and lightly loaded. The test estimates the rate reaching this browser window from animation-frame timing. It does not read the monitor datasheet, cable, port, panel maximum or in-game FPS.
Why does the result change when I move the window to another monitor?
The result follows the display where the browser window is rendered. If one display is 60Hz and another is 165Hz, moving the window can change the browser cadence. Put the window fully on the monitor you want to test and run the measurement again.
Why might Safari show 60Hz on a 120Hz display?
First check Low Power Mode, the selected display refresh rate and whether you are testing in Safari itself rather than an in-app browser or saved web app. Safari and WebKit behavior can vary by operating-system and browser version. Some versions expose page-rendering preferences in Feature Flags, but the name and availability can change.
Can this detect FreeSync or G-Sync?
No. Variable timing can appear for many reasons, including browser load, power behavior or display scheduling. This test does not identify FreeSync, G-Sync, VRR brand support, GtG response time or MPRT.
Does this work with 240Hz, 360Hz and higher-refresh displays?
It can report high browser-visible rates when the operating-system mode, display path and browser actually deliver them to this window. Compare the result with the selected OS rate. If a 240Hz display produces a stable 144Hz result, check the selected resolution and refresh mode before assuming a hardware fault.