How to check 240 Hz
Open this page on the 240 Hz monitor, keep the window there and wait two seconds. The reading should settle on 240 with a frame time of 4.17 ms, and the verdict under it turns to Pass. If it shows Below, the list under the verdict covers the setting, the port and, on Windows at a standard resolution, the data rate your resolution needs at 240 Hz. For a monitor rated 280, 360 or 480 Hz, pick that rate in the Rated refresh rate list.
240 against 120 and 60 fps
The motion test on this page compares every refresh with 120 and 60 fps instead of 60 and 30. Both divide evenly into 240, so the 120 fps row is drawn on every second refresh and the 60 fps row on every fourth, with no uneven steps of its own. At the default 960 pixels per second, the object moves 4 pixels per refresh at 240 Hz, 8 at 120 fps and 16 at 60 fps: the shorter the step, the less it smears as your eye follows it. Pick a faster speed to make the difference easier to see.
Why 240 Hz monitors stop at 144 or 165 Hz
The bandwidth needed grows with resolution and refresh rate, and 240 Hz is where older links run out. With VESA’s tightest standard timing:
- 1080p at 240 Hz needs about 14 Gbps of video: HDMI 2.0 only just carries it, DisplayPort 1.2 with room to spare.
- 1440p at 240 Hz needs about 24.6 Gbps: DisplayPort 1.4 carries it at 8 bits per colour with about 5% to spare, and 10-bit HDR needs a full-bandwidth HDMI 2.1 port, DisplayPort 2.1 or compression.
- 4K at 240 Hz needs about 55 Gbps, more than HDMI 2.1’s 42.7 Gbps: it takes Display Stream Compression (DSC), which DisplayPort 1.4 and HDMI 2.1 both support as an option, or DisplayPort 2.1 at its fastest UHBR20 rate.
So a 1440p 240 Hz monitor on an HDMI 2.0 input tops out around 144 Hz, and on a graphics card with only DisplayPort 1.2 around 170 Hz, even though the panel can do more. The table further down has the figures for each resolution.
Other things that cap the reading
Safari holds web pages near 60 fps, so use Chrome or Firefox. Firefox follows the display unless layout.frame_rate in about:config is set to a fixed number instead of -1. Energy Saver in Chrome and efficiency mode in Edge can hold animations to about 30 fps. The verdict shows these caps as Browser limit rather than Below, because they hide the monitor’s real rate. With an NVIDIA card and variable refresh turned on, NVIDIA says the refresh rate is set to the display’s highest automatically, so it should still read 240.
For a 144 Hz screen, use the 144 Hz test; for an overclocked monitor, the frame skipping test; for phones, the iPhone and Android tests. The plain refresh rate test works for any display.
What 240 Hz needs from the connection
The video data a monitor needs grows with its resolution and refresh rate. This table works it out for 240 Hz with VESA’s reduced-blanking timing (CVT-RB2), the tightest standard timing, and compares it with what each connection carries after its line coding. It shows the oldest version that carries the signal uncompressed at 8 bits per colour, then at 10 bits (HDR).
The graphics card’s output and the monitor’s input must both support that version, with a cable certified for the speed: High Speed HDMI (10.2 Gbps), Premium High Speed (18 Gbps), Ultra High Speed (48 Gbps).
| Resolution at 240 Hz | Video data | DisplayPort | HDMI |
|---|---|---|---|
| 1080p1920 × 1080 | 14.0 Gbps10-bit: 17.5 Gbps | 1.2 or newer10-bit: 1.4 or newer | 2.0 (only just) or newer10-bit: 2.1 |
| 1440p2560 × 1440 | 24.6 Gbps10-bit: 30.8 Gbps | 1.4 or newer10-bit: 2.1 UHBR10 or newer, or 1.4 with DSC | 2.1 |
| Ultrawide 1440p3440 × 1440 | 32.8 Gbps10-bit: 41.0 Gbps | 2.1 UHBR10 or newer, or 1.4 with DSC10-bit: 2.1 UHBR13.5 or newer, or 1.4 with DSC | 2.110-bit: 2.1 (only just) |
| 4K3840 × 2160 | 54.8 Gbps10-bit: 68.6 Gbps | 2.1 UHBR20 or 1.4 with DSC | DSC only |
“Only just” means the signal fits with the standard timing but leaves under 5% to spare, so a monitor with looser timings of its own may stop short on that link: its manual has the final word. “With DSC” and “DSC only” refer to Display Stream Compression, which VESA added in DisplayPort 1.4 and describes as visually lossless; the monitor and graphics card both have to support it.
HDMI 2.1 ports run at 18 to 48 Gbps; the figures assume a full 48 Gbps port: check the monitor’s and card’s specs. Every HDMI 2.1 feature is optional, so a port sold as HDMI 2.1 may run no faster than HDMI 2.0.
| Connection | On the wire | Left for video |
|---|---|---|
| HDMI 1.4 | 10.2 Gbps | 8.16 Gbps |
| HDMI 2.0 | 18 Gbps | 14.4 Gbps |
| HDMI 2.1 | 48 Gbps | 42.67 Gbps |
| DisplayPort 1.2 | 21.6 Gbps | 17.28 Gbps |
| DisplayPort 1.4 | 32.4 Gbps | 25.92 Gbps |
| DisplayPort 2.1 (UHBR10) | 40 Gbps | 38.69 Gbps |
| DisplayPort 2.1 (UHBR13.5) | 54 Gbps | 52.22 Gbps |
| DisplayPort 2.1 (UHBR20) | 80 Gbps | 77.37 Gbps |
Sources: HDMI Licensing Administrator (HDMI 1.3 announcement: 340 MHz, 10.2 Gbps, the speed HDMI 1.4 keeps; HDMI 2.0: 18 Gbps; cable types: 10.2, 18 and 48 Gbps; HDMI 2.1 labelling: optional features) and VESA (DisplayPort 2.0 announcement: 25.92 Gbps of payload for DisplayPort 1.4, 77.37 Gbps for UHBR20). HDMI up to 2.0 and DisplayPort 1.x lose 20% to 8b/10b coding, HDMI 2.1’s fixed-rate link 11% (16b/18b over 3 or 4 lanes of 3 to 12 Gbps, Granite River Labs) and DisplayPort 2.1 about 3%.