Refresh Rate Tester

About Refresh Rate Tester & FPS Counter

Measure your monitor's actual refresh rate and FPS using browser APIs. This tool uses requestAnimationFrame() to detect display frequency accurately. Perfect for checking if your monitor is running at 60Hz, 120Hz, 144Hz, 240Hz, or higher refresh rates.

How do I test my monitor's refresh rate in a browser?

Press Start Test and leave this browser tab in the foreground for at least five seconds. The tool calls requestAnimationFrame() in a tight loop and timestamps each callback with performance.now(). Dividing 1000 by the median interval between callbacks gives the effective Hz, which converges to your monitor's true refresh rate within a few hundred frames. Do not switch tabs or minimize the window — Chromium, Firefox, and Safari all throttle background tabs to 1 Hz or pause them entirely. Close GPU-heavy applications (video editors, games, Discord overlays) so the browser's render thread is not starved. After five to ten seconds the average value should match a standard rate such as 60, 75, 120, 144, 165, 240, or 360 Hz.

What is the difference between 60 Hz, 144 Hz, and 240 Hz?

Refresh rate is how many distinct frames per second your panel can present. 60 Hz repaints every 16.67 ms and is fine for office work and most video. 144 Hz repaints every 6.94 ms, halves perceived motion blur on scrolling text, and is the sweet spot for esports titles such as CS2, Valorant, and Overwatch. 240 Hz repaints every 4.17 ms and delivers a measurable but smaller jump — competitive players value the reduced input-to-photon latency more than the visual smoothness. Diminishing returns kick in hard above 240 Hz: 360 Hz and 540 Hz panels exist but mostly benefit professional tournament players. Your GPU must also produce frames at the panel's rate or VRR will fill the gaps.

Why does my 144 Hz monitor read as 60 Hz here?

Three culprits cover almost every case. First, the operating system display setting is still at 60 Hz — Windows requires you to open Settings, System, Display, Advanced display, and pick the higher rate explicitly per output. Second, the cable cannot carry the bandwidth: HDMI 1.4 caps 1080p at 120 Hz and 1440p at 60 Hz; you need HDMI 2.0+ or DisplayPort 1.2+ for 144 Hz at 1440p. Third, browsers running on integrated GPUs sometimes lock the compositor to 60 Hz to save power — switch to a Chromium-based browser with hardware acceleration enabled, plug the laptop in, and disable battery saver. macOS users on ProMotion displays must also disable Low Power Mode for the full 120 Hz.

What is frame time and how is it different from FPS?

FPS is the count of frames delivered in one second; frame time is the interval between two consecutive frames in milliseconds. They are reciprocals: frame time in ms equals 1000 divided by FPS. Frame time is the more honest metric because a stable 144 FPS average can hide 30 ms stutter spikes that ruin the feel of a game. The live chart on this tool plots every frame's interval, so a flat horizontal line at 6.94 ms means a perfectly smooth 144 Hz, while a sawtooth pattern reveals dropped frames, compositor jank, or thermal throttling. Aim for frame time variance under one millisecond — that is the threshold below which most humans no longer perceive judder.

Does this tool work with G-Sync, FreeSync, or VESA Adaptive-Sync?

Yes, and you will see fluctuating values because that is exactly what those technologies do. Variable Refresh Rate lets the monitor wait for the GPU instead of forcing the GPU to wait for the monitor, eliminating tearing and stutter inside the VRR window (typically 48 to 144 Hz or 30 to 240 Hz). Because the browser does not render at a perfectly steady cadence, an idle page over VRR may bounce between 90 and 144 Hz second-to-second, which is correct behavior. To measure the panel's hardware maximum, temporarily disable VRR in the NVIDIA Control Panel, AMD Adrenalin, or your monitor's OSD, then rerun the test. Re-enable it for daily use.

How precise is requestAnimationFrame() compared to a hardware Hz meter?

Browser requestAnimationFrame() ticks are aligned to the compositor's VSync, so on a quiet system the measured rate matches the panel within roughly 0.5 Hz. The main precision limit is performance.now()'s timer resolution: modern browsers clamp it to 5 microseconds (Chrome) or 1 millisecond in cross-origin isolated contexts to mitigate Spectre side-channel attacks. A laboratory-grade photodiode plus oscilloscope is still needed to certify true panel response time and the gray-to-gray transitions that ULMB and DyAc strobing depend on. For verifying that the operating system, cable, and driver chain are delivering the rate you paid for, this tool is accurate enough — it catches every misconfiguration short of subpixel response timing.

What is ULMB and why does it matter at high refresh rates?

Ultra Low Motion Blur (NVIDIA) and its AMD equivalent DyAc strobe the panel's backlight in sync with each frame, blanking the display between refreshes so the eye sees a sharp frame instead of a smeared one. Sample-and-hold LCDs blur in proportion to frame time, so a 60 Hz panel blurs roughly twice as much as 120 Hz even at infinite GPU FPS. ULMB at 120 Hz can equal the motion clarity of a non-strobed 240 Hz screen. The trade-off is reduced brightness (often 30 to 50 percent dimmer) and incompatibility with most VRR implementations — you pick one or the other. Browser tools cannot detect strobing because the camera and the panel are not in sync; use the UFO Test pursuit-camera method to verify.

Why does Safari on iPhone show 60 Hz on my 120 Hz ProMotion screen?

Apple gates the full 120 Hz ProMotion refresh behind an explicit CADisplayLink preferredFrameRateRange opt-in for native apps and a CSS prefers-reduced-motion plus high-performance hint for the web. Until Safari 16, web pages were locked to 60 Hz to save battery; Safari 16 and later raise the cap to 120 Hz only when the page is actively animating with requestAnimationFrame() and the device is not in Low Power Mode. If the test reads 60 Hz, open Settings, Battery, and turn Low Power Mode off, then make sure you are in fullscreen Safari rather than an in-app webview (Twitter, Slack), which inherits the host app's frame-rate ceiling and rarely enables ProMotion.

How do I export and interpret a measured session for a QA report?

Run the test for at least five to ten seconds, click Stop, then use Export CSV or Export JSON. Both files carry a stats header (min, max, avg, 1% low Hz, jitter, mean frame time, sample count, dropped frames) followed by every captured frame as index, timestamp (ms), frame time (ms) and instant Hz, so you can attach the raw series to a repair ticket or diff two machines.

How to read it for pass/fail:
- Avg Hz should sit within ~1 Hz of the rated rate; a large gap means the OS, cable or driver is not delivering the panel maximum.
- 1% Low Hz is the worst-case sustained rate (the slowest 1% of frames). If a 144 Hz panel shows a 1% low of 90 Hz, something is intermittently starving the render thread.
- Jitter is the frame-time standard deviation in milliseconds. Under ~1 ms is smooth; a rising value, or a sawtooth pattern on the chart, points to a marginal cable, throttling, or a compositor fighting another app.
- Dropped Frames counts intervals longer than 100 ms that were excluded as outliers — anything above zero on a foreground tab is a red flag worth investigating.

Is the measured value GPU FPS, and which monitor does it test?

The number this tool reports is the compositor / display refresh rate derived from requestAnimationFrame intervals, not your GPU's rendered FPS. On a steady system the two coincide, but on VRR or power-throttled setups they diverge, which is why the value is labelled refresh rate, not FPS. The tool can never exceed the rate the browser grants the tab, so a backgrounded tab is throttled to roughly 1 Hz and the reading becomes meaningless — that is why a warning appears and hidden-tab samples are flagged invalid.

For reproducibility, remember the tool measures only the display the browser window currently lives on. On a multi-monitor setup, drag the window fully onto the panel under test (a 60 Hz secondary and a 144 Hz primary will report different rates), avoid straddling two screens, and rerun. It cannot detect which physical port, cable or GPU is involved — only the effective rate the operating system is presenting to that window.

Key Features

• Real-time refresh rate measurement (raw measured Hz, no rounding)
• Accurate Hz measurement (60Hz, 144Hz, 240Hz, 360Hz, etc.)
• Frame time analysis in milliseconds
• Session statistics: min / max / avg / 1% low Hz, jitter, dropped frames
• One-click CSV and JSON export of the captured frame-time series
• Live chart visualization with reference lines
• Sample collection tracking (full session capture)
• Test duration timer
• Common refresh rates reference guide
• VRR-aware (shows refresh-rate fluctuation; cannot detect the VRR tech itself)
• Works on all devices (desktop, laptop, tablet)
• Supports all monitor types (LCD, LED, OLED)
• 100% client-side testing (no server needed)
• No installation required (browser-based)
• Privacy-friendly (no data collection)
• Free to use forever
• Mobile responsive design