Why does it show 60 Hz on my 144 Hz monitor?

The most common reason is that the operating system is set to 60 Hz. Check the display settings and choose the highest rate. Some laptops also drop to 60 Hz on battery, and some browsers cap the frame rate when the window is not focused.

Can a browser measure the refresh rate exactly?

No. It can only count how often it is allowed to draw, which usually matches the refresh rate but can be lower. Treat the number as a good estimate, not a hardware measurement.

Refresh Rate Test

Your browser draws a new frame each time the display refreshes. Counting those frames gives a good estimate of the refresh rate, and a moving bar shows how smooth motion looks at that rate.

—Hz

Not measured yet

The estimate comes from how often the browser paints, not from the display hardware. Battery saving, browser limits and background load can lower it.

Runs entirely in your browser. Nothing is uploaded or stored.

How to use

Close other heavy tabs and, on a laptop, plug in the charger so power saving does not cap the frame rate.
Press Start measuring and keep the tab in the foreground for three seconds. The estimate and the closest common rate update as it runs.
Compare the estimate with the closest common rate shown under it, and check the dropped-frame count.
Press Open motion test to watch a bar move at that rate. Smooth, evenly spaced motion means frames are not being dropped; Pause freezes it so you can look at one frame.

What this test can detect

The refresh rate your browser is currently running at, for example 60, 75, 120, 144, 165 or 240 Hz.
A monitor that is set to a lower rate than it supports (check your operating system display settings).
Dropped or uneven frames, which show up as jitter in the motion test.

Important

The estimate comes from how often the browser paints, not from the display hardware. Battery saving, browser limits, background load and some operating systems cap this below the true refresh rate.
On a multi-monitor setup the estimate usually reflects the screen the window is on, but some browsers use the main display's rate for every window.
A rate that reads slightly off, for example 59.9 or 143.8 Hz, is normal rounding, not a fault.

Questions

Why does it show 60 Hz on my 144 Hz monitor?: The most common reason is that the operating system is set to 60 Hz. Check the display settings and choose the highest rate. Some laptops also drop to 60 Hz on battery, and some browsers cap the frame rate when the window is not focused.
Can a browser measure the refresh rate exactly?: No. It can only count how often it is allowed to draw, which usually matches the refresh rate but can be lower. Treat the number as a good estimate, not a hardware measurement.