Refresh rate test

Measures the Hz you are receiving right now, not the ones on the box. With a motion test and a full display readout.

Measuring…

Frame time — ms

Stability — ± 0.00 ms

Frames measured 0

Motion test Speed

Follow the square with your eyes. At 60 Hz you see a stepped trail; at 120 or more the movement reads as continuous. That is the difference the number alone cannot convey.

Common rates

60 Hz75 Hz90 Hz120 Hz144 Hz165 Hz240 Hz

If your measurement does not match what your monitor advertises, it is nearly always that the system is not set to its maximum, or the cable cannot carry it.

Why it might read lower than expected

The system is set below the monitor’s maximum
An older HDMI or DisplayPort cable cannot carry that resolution and rate together
The laptop is on battery and has dropped the rate to save power
The browser throttles to 60 in a background tab or under heavy load
An adaptive display lowers the rate when the content is not changing

Generated right here, in your browser. What you type never leaves your device.

Keep going with Reaction time test Screen test Monitor calibration Dead pixel test

A 144 Hz monitor does not always deliver 144. The system may be set to 60, the cable may not carry it, or a laptop may have dropped the rate on battery. This test measures what your screen is doing at this moment, which is the only figure that matters.

The browser offers no direct way to ask, so it is inferred: request a frame, time how long until the next arrives, and the rate is the reciprocal of that interval. With two hundred samples the figure settles firmly.

Below there is a motion test, because the number alone does not convey the difference. At 60 Hz a moving object leaves a stepped trail; at 120 or more the movement reads as continuous. Seeing it is more convincing than reading it.

Manual

How to use it

1
Wait a few seconds

Measuring starts on its own. The first frames are usually irregular while the page finishes loading, so the number settles after a couple of seconds.
2
Watch stability, not just the Hz

If it says "variable", the rate is fluctuating. That may be an adaptive display doing its job, or the browser throttling under load.
3
Close other tabs and retry

A heavy background tab can steal frames and drag the measurement down. If closing them raises it, your monitor was not the problem.
4
Try the laptop plugged in

Many laptops drop to 60 Hz on battery to save power. It is the commonest reason a 120 Hz screen measures half.
5
Use the motion test

Raise the speed and follow the square with your eyes rather than holding your gaze still. That is where the difference between 60 and 144 becomes obvious.

In depth

Things worth keeping in mind

Hz and FPS are not the same thing

Hertz is how many times a second your screen draws a new image. FPS is how many images a second the computer produces. They are independent rhythms that only coincide when something synchronises them.

If the computer generates 200 images a second and the screen can only show 60, more than two thirds are discarded. If it generates 40 on a 144 Hz screen, some frames repeat. Both screen tearing and visible stutter come from that mismatch.

Hz: what the screen can show
FPS: what the computer produces
More FPS than Hz: images are discarded
Fewer FPS than Hz: frames repeat

Adaptive refresh

FreeSync, G-Sync and ProMotion make the screen wait for the computer rather than the other way round: the monitor refreshes when a new image is ready, within a range. That removes tearing without the latency classic synchronisation added.

For this test it has an odd consequence: if your display is adaptive, the measurement may read "variable" and be perfectly normal. On a ProMotion phone the rate also drops on its own when the content is still, so you can see 60 on a 120 Hz screen with nothing wrong.

When more Hz matters and when it does not

The jump from 60 to 120 is noticeable, and clearly so: in page scrolling, in cursor movement, in anything travelling sideways. From 120 to 240 the difference exists but is far subtler, and you only benefit if the machine can sustain that many frames.

For reading, writing or watching video, 60 Hz remains perfectly sufficient. Film is shot at 24 images a second and nobody calls it unwatchable. Where it genuinely changes things is fast games and the overall feel of system responsiveness.

Why your cable may be the limit

Resolution and refresh rate consume bandwidth together, so a cable can be more than enough for 1080p at 144 Hz and fall short for 4K at 144. When it cannot manage, the system does not warn you: it simply offers the highest combination it can sustain.

HDMI 1.4 reaches 4K but only at 30 Hz. HDMI 2.0 gets 4K at 60. For 4K at 120 you need HDMI 2.1 or DisplayPort 1.4, with cables that genuinely meet the specification — not all that advertise it do.

HDMI 1.4 · 4K at 30 Hz · 1080p at 144 Hz
HDMI 2.0 · 4K at 60 Hz
HDMI 2.1 and DisplayPort 1.4 · 4K at 120 Hz or more

History

From CRT flicker to 240 Hz

Refresh rate began as a phosphor problem. In a cathode ray tube the beam lights a dot that starts fading immediately, so the whole screen has to be retraced many times a second or the eye perceives flicker. Below about 60 Hz it was exhausting to look at.

Analogue television fixed 50 or 60 fields a second depending on the country, and not on visual grounds but for engineering convenience: it matched the mains frequency, which vastly simplified the circuits and avoided visible interference.

Early LCDs went backwards. Because a pixel stays lit until told otherwise, flicker disappeared and 60 Hz was considered sufficient for nearly two decades. The problem became something else: how long a pixel takes to change colour, which produced smearing.

Gaming monitors broke that stagnation from about 2010, first at 120 Hz and then 144, 240 and beyond. And from 2017 phones followed the same path, to the point that a high-end phone screen today refreshes faster than most desktop monitors.

60 Hz: The standard for decades
16.7 ms: One frame at 60 Hz
6.9 ms: One frame at 144 Hz
2017: High refresh arrives on phones

How it works

Measuring something the browser will not tell you

There is no function that returns the refresh rate. What does exist is a frame request: you ask the browser to run something just before the next repaint, and it calls you in step with the display.

The measurement follows from that. Record the moment of each call, compute the gap to the next, and the rate is a thousand divided by that gap in milliseconds. A 60 Hz monitor gives gaps of 16.7 ms; a 144 Hz one, 6.9.

The median of two hundred samples is used rather than the mean, and that choice matters: a single stutter while the page finishes loading would drag an average, while an extreme value barely moves a median.

The spread of those gaps is the other interesting figure. A fixed-rate screen produces near-identical gaps, so the spread is minimal. An adaptive one varies on purpose, and an overloaded tab varies by accident — the number cannot tell them apart, but knowing which is your case can.

There is an honest limit to all this: the browser never delivers frames faster than the display, but it can deliver them slower when saturated or when the tab loses focus. So the test measures what you are receiving, not what your monitor is capable of.

By hand

Checking the settings outside the browser

If the measurement comes in below what your monitor advertises, the problem is almost always system configuration. It takes a minute to check.

1

Settings → System → Display → Advanced display. There is a dropdown of available rates. Pick the highest and apply.
2

System Settings → Displays. Hold Option while clicking Scaled to reveal the rates the system hides by default.
3

The same monitor may accept more Hz over DisplayPort than over HDMI. If you have both, try the other port before blaming the monitor.
4

If it drops on battery and rises plugged in, that is power management rather than a fault. It can be changed in the system power profile.
5

The system can claim 144 and deliver something else. The measured figure is what counts.

Diagnosis

If something is not working

Symptom:It reads 60 Hz and my monitor is 144

Likely cause:: The system is almost always set to 60: it rarely selects the maximum by itself when a monitor is connected.
What to do:: On Windows, open Advanced display settings and pick 144 in the dropdown. On macOS, hold Option while clicking Scaled under Displays. Come back and check, because the system can say one thing and deliver another.

Symptom:The high rate does not appear in the system options

Likely cause:: The cable or the port cannot carry that combination of resolution and rate.
What to do:: Try DisplayPort if you have it, which usually carries more than HDMI. On HDMI you need 2.1 for 4K at 120. And try another cable: many advertise a specification they do not meet.

Symptom:It says variable instead of a steady figure

Likely cause:: Either you have an adaptive display doing its job, or the browser is throttling under load.
What to do:: Close other tabs and retry. If it still varies and your monitor has FreeSync or G-Sync, that is normal. On a phone with an adaptive display, likewise.

Symptom:On battery it measures half

Likely cause:: Power management lowers the rate to extend charge. This is not a fault.
What to do:: Plug the machine in and retry. If you want high Hz on battery, it can be set in the power profile, at the cost of runtime.

Symptom:The reading drops when I move the mouse or type

Likely cause:: The page is competing for resources, so the browser delivers frames more slowly.
What to do:: Leave the machine alone for a few seconds and measure again. It is also the reason to wait for the number to settle before trusting it.

Symptom:My 120 Hz television measures 60

Likely cause:: Many televisions refresh the panel at 120 but only accept 60 over the input, or apply frame interpolation.
What to do:: Look for game or PC mode in the television settings, which disables the processing. And check the input is set for high-speed signal, which many models leave off by default.

Trivia

Things worth knowing

60 Hz comes from the wall socket

Analogue television synchronised with the mains frequency — 60 Hz in the Americas, 50 in Europe — because it avoided visible interference and simplified the design. That 1930s decision still shapes the standard.

Film runs at 24 images a second

And reads as smooth thanks to the motion blur the camera itself introduces. A game at 24 FPS is unplayable because it produces sharp images, with no such blur.

Your phone probably refreshes faster than your monitor

120 Hz screens have been common in phones for years, while most desktop monitors sold are still 60.

A background tab is throttled on purpose

Browsers cut frame requests to once a second in hidden tabs to save battery. That is why this test only measures properly while you are looking at it.

More Hz cuts latency, not just judder

At 60 Hz a new image takes up to 16.7 ms to appear. At 240 Hz, 4.2. Part of the competitive advantage of high refresh is not smoothness but that head start.

Questions

Frequently asked questions

Is this measurement reliable?

Fairly, with one caveat: it measures the frames the browser is delivering, which never exceed the display’s but can fall below if the machine is loaded. With the tab in the foreground and nothing heavy running, the figure is faithful.

What is the difference between Hz and FPS?

Hz is how often the screen refreshes; FPS is how many images the computer produces. More FPS than Hz means images are discarded; fewer means frames repeat.

Is going from 60 to 144 really noticeable?

In motion, yes and clearly: scrolling a page, moving the cursor, fast games. For reading or video the difference is minimal. Use the motion test and raise the speed, which is where it becomes obvious.

Why does my phone read variable?

Because many modern displays lower the rate by themselves when content is still, to save battery. Seeing 60 on a 120 Hz screen in that situation is expected, not a fault.

Can it measure more Hz than my screen has?

No. The browser synchronises frames with the actual refresh, so the measurement never exceeds what the display delivers. It can fall below, never above.

Does it work on a television?

Yes, from its browser or by connecting a computer. Bear in mind many televisions refresh the panel at 120 but only accept 60 over the input, so the reading may be correct even though the panel is capable of more.