Is your screen really running at 120 Hz or 144 Hz?

A 120 Hz screen shows 120 frames a second only when two things are true: the display is set to 120 Hz, and the computer is sending 120 frames a second. If either one is missing, you see less. The refresh rate test measures the second part, the frames the browser actually delivers, and reports the nearest common rate. It can point at a problem, but it cannot read the settings or the cable directly.

Hz and fps are different things

Hz (hertz) is how many times per second the screen refreshes its image. fps (frames per second) is how many complete images the computer produces. Smooth motion needs the two to match. A 120 Hz panel fed 60 frames a second typically shows each frame twice, so motion looks like 60 frames. A 60 Hz panel cannot show 120 frames of motion at all, because it refreshes only 60 times a second.

Where the setting lives

The rate is chosen in the operating system, usually in the display settings. Menu names change between versions, so search the settings for "refresh rate" if the path below differs.

• Windows. In Windows 11, open Settings, then System, then Display, then Advanced display. The refresh rate is picked from a drop-down there. Windows 10 offers the same choice in a slightly different place.
• macOS. Open System Settings and choose Displays. Many Macs with ProMotion adjust the rate automatically, so there may be no fixed choice. Some external monitors offer a refresh rate option in the same panel.
• Android. Phones with high-refresh screens usually have a setting in Display, often called Smooth display or Motion smoothness, that offers a standard and a high rate. The name differs by manufacturer.
• iPhone. ProMotion adjusts the rate automatically, and there is no everyday setting to pick 120 Hz. The Accessibility settings include an option to limit the frame rate, which makes the phone run at a lower rate on purpose.

Cables, ports and adapters

A monitor can run at a high rate only if the cable and port can carry the signal. The bandwidth needed grows with resolution, refresh rate and colour depth. A 4K screen at 144 Hz needs far more capacity than a 1080p screen at 60 Hz. Older cables and ports cannot carry 4K at high refresh rates. Recent DisplayPort and HDMI 2.1 connections can, and at the top settings they may use compression (DSC) to fit the data through the link. A higher resolution uses more of the same bandwidth, so check the screen resolution too if a high rate will not stick.

If you set a high rate and the monitor quietly falls back to 60 Hz, the cable or port is the likely cause. Use the cable that came with the monitor, or one certified for the version you need. Connect directly where you can, because cheap USB-C hubs and docks often cap the output. Some monitors reach their top rate on only one of their ports, so check the input menu too.

Battery saver and power modes

Laptops and phones often lower the refresh rate on battery to save power. Battery saver and low-power modes can cap it at 60 Hz, sometimes with no obvious message. Plug the device in and run the test again before you judge the screen. Browsers can also throttle animation in background windows, and this test pauses when its tab is hidden, so keep the test tab in the foreground while it runs.

Variable refresh rate

Variable refresh rate (VRR) changes the screen's rate to match the frames being produced. It appears under several names: adaptive sync, ProMotion on Apple devices, and G-Sync or FreeSync on PC monitors. When the picture is still, the rate can drop well below its maximum to save power, and it climbs again when something moves. A test that runs while nothing changes may report a lower number than the peak. Keep the moving tile running, or keep the mouse moving, so the test sees the full rate.

What the browser test can and cannot tell

The test counts frames the browser draws, using requestAnimationFrame, the browser's hook for drawing in step with the screen. It takes the median of recent frame intervals, so single stutters do not dominate, and it reports the nearest common rate from 60 to 360 Hz. It also shows the average frame time and the number of long frames, which helps you judge whether motion is smooth.

It cannot read the panel's settings, the cable type or the monitor's maximum. A reading of 60 means the browser delivered about 60 frames a second while you measured. It does not prove the display is limited to 60. If the setting says 144 Hz and the test reads 60, look at the power mode, the cable, the browser's hardware acceleration and any frame limiter in games or other apps. If the test reads 120 and the setting says 120, that is a good sign, but it does not show that every app runs smoothly.

Quick answers

Why does the test say 60 on my 144 Hz monitor? Usually the setting is still 60, a power mode is capping the rate, or the cable or hub cannot carry the higher mode. Check those in that order.

Does a high number prove my screen works? It shows the browser is receiving that many frames. It does not check colour, uniformity or dead pixels. For those, use the dead pixel test.

Why does the test show a lower number when I am not moving? Variable refresh rate may drop when nothing changes. Keep the moving tile running to see the peak.