HDMI 2.1 max refresh rate at 1440p and 4K

It depends on the link speed the port really runs, and the words "HDMI 2.1" do not tell you which. A full 48 Gbps HDMI 2.1 port carries 1440p up to about 384 Hz and 4K up to about 191 Hz at 8-bit colour, with no compression. A port that only runs the older TMDS signalling can still be sold as HDMI 2.1. That port stops at 1440p 147 Hz and 4K 68 Hz, the same as HDMI 2.0. That is why an "HDMI 2.1" monitor can stop at 144 Hz.

What HDMI 2.1 is, and why the name does not give the speed

HDMI 2.1 is the HDMI version that added a faster way to send the picture. The old way is TMDS (Transition Minimised Differential Signalling). It sends data on three lanes, which are separate wire pairs side by side. On HDMI 2.0, TMDS tops out at 18 Gbps.

The new way is FRL (Fixed Rate Link). Texas Instruments' HDMI 2.1 application note says FRL turns the three TMDS data lanes into FRL lanes 0 to 2, and the old clock lane into lane 3. TI lists six FRL speeds: 3 or 6 Gbps per lane on 3 lanes, and 6, 8, 10 or 12 Gbps per lane on 4 lanes. Only the last one is the 48 Gbps people associate with HDMI 2.1.

Here is the catch. HDMI.org, the HDMI licensing body, told TFTCentral in December 2021 that "HDMI 2.0 no longer exists". It said the features of HDMI 2.0 "are now a sub-set of 2.1". And it said all the new HDMI 2.1 features are optional, which "includes FRL, the higher bandwidths, VRR, ALLM and everything else". So a port with nothing but HDMI 2.0 speed can carry the HDMI 2.1 name.

Not every bit on the wire is picture. TMDS sends 8 bits as 10, so 80% is picture. FRL uses 16b/18b encoding, which TFTCentral gives as 88.8% efficient. What is left for the picture is the payload:

Note the two 18 Gbps rows. FRL on three 6 Gbps lanes has the same raw rate as TMDS, but carries 11% more picture, because less of it goes on encoding.

A mode needs its pixel clock times 24 bits per pixel (8-bit colour) or 30 bits (10-bit). The pixel clock is how many pixels the link sends per second. It counts the visible pixels plus blanking, the unseen gap a video signal leaves around each line and frame.

Top refresh rate at each HDMI 2.1 link speed

We worked out pixel clocks with an open implementation of VESA's CVT 1.2 timing formula, in reduced blanking v2 mode. These are the same clocks as our HDMI 2.0 page and our DSC and bandwidth article. We stepped the refresh up one hertz at a time until the mode no longer fit the payload.

The TMDS row is the HDMI 2.0 limit, to the hertz. Some common modes, against each link:

• 1440p 165 Hz needs 16.30 Gbps at 8-bit. TMDS cannot carry it. FRL on three 6 Gbps lanes misses by 2%. The 24 Gbps tier and up carry it.
• 1440p 240 Hz needs 24.62 Gbps at 8-bit. The 24 Gbps tier stops at 211 Hz, so it needs 32 Gbps. At 10-bit it needs 30.77, so 40 Gbps.
• 1440p 360 Hz needs 39.37 Gbps at 8-bit. Only the full 48 Gbps link carries it, using 92%. At 10-bit it needs 49.21, more than any HDMI 2.1 link carries without compression.
• 4K 120 Hz needs 25.82 Gbps at 8-bit (32 Gbps tier) and 32.27 at 10-bit (40 Gbps tier).
• 4K 144 Hz needs 31.35 Gbps at 8-bit (40 Gbps tier) and 39.19 at 10-bit (48 Gbps only).

Worked case: why the Alienware AW2725DF stops at 144 Hz over HDMI

A Dell community thread from March 2024 asks this exact question. The poster's AW2725DF is a 27-inch 1440p QD-OLED rated for 360 Hz. They ask why its HDMI 2.1 port stops at 1440p 144 Hz "when the spec for 2.1 clearly states that 48gbps of bandwidth is available". Here is how the numbers read.

TFTCentral's review lists two DisplayPort 1.4 inputs and one HDMI port. Dell calls that port HDMI 2.1, but, per TFTCentral, goes on to say it runs at "TMDS speeds". TFTCentral notes it "does not have the new FRL bandwidth" and gives its HDMI refresh as 48 to 144 Hz.

So take the TMDS row. It carries 14.40 Gbps of picture. 1440p 360 Hz needs 39.37 at 8-bit, about 2.7 times that. 240 Hz needs 24.62 and 165 Hz needs 16.30. Neither fits. 144 Hz needs 14.08, which fits with 2% to spare. The top is 147 Hz, so 144 is the highest standard step. The cap is exactly what TMDS allows.

Now suppose the same port ran full 48 Gbps FRL. 360 Hz at 8-bit would fit with no compression. Over DisplayPort 1.4 the monitor needs DSC (Display Stream Compression) for 360 Hz. DSC squeezes the picture so a mode fits a slower link. That matters to the poster, who says DSC "causes issues with features like DLDSR". Which features DSC switches off is in the DSC article.

48 Gbps or 18 Gbps: which HDMI 2.1 is right

Two readings circulate. One says HDMI 2.1 means 48 Gbps, so any HDMI 2.1 port should run any mode up to that. The other says HDMI 2.1 is just a name, and the speed can be anything down to HDMI 2.0.

The second is right, by the licensing body's own rules. HDMI.org told TFTCentral that FRL and the higher bandwidths are optional. TFTCentral concluded that the Xiaomi 24.5-inch 240 Hz monitor, which it found listing HDMI 2.1 ports that only run TMDS, was labelled correctly by HDMI.org's definition. Xiaomi's product page, as TFTCentral quotes it, says "The HDMI 2.1 interface of this product supports the TMDS protocol".

The 48 Gbps reading persists for a fair reason. It is the headline figure. HDMI.org's page says the Ultra High Speed cable from HDMI 2.1 is "applicable for system configurations supporting up to 48Gbps maximum bandwidth". And in 2021 TFTCentral wrote that nearly every display marketed as HDMI 2.1 had at least the higher bandwidth, Xiaomi being the one exception it had seen. The AW2725DF, reviewed in 2024, shows the exception did not stay alone.

How to tell what your HDMI 2.1 port does

Read the refresh the spec sheet gives for the HDMI input, not the version number. Then compare it with the table.

• Above the TMDS row means FRL. HDMI.org, quoted by TFTCentral, says FRL "is necessary to achieve the higher uncompressed resolutions such as those above 4k60", and is "also required for compressed video transport". So 1440p above 147 Hz over HDMI means FRL, with or without compression.
• MSI MAG 271QPX QD-OLED. MSI's datasheet lists "2 x HDMI™ 2.1 (WQHD@360Hz)". The MPG 271QRX datasheet uses the same words. At 8-bit with no compression, only the 48 Gbps tier carries that. Neither sheet says whether DSC is used.
• ViewSonic XG273B-2K-OLED. ViewSonic's page lists "2560×1440 @ 360Hz 10bit RGB" over HDMI 2.1. At standard timing that needs 49.21 Gbps, more than 42.67. So that mode uses DSC or a much shorter blank than standard. The page does not say which.
• The word TMDS or FRL. Some makers print it, as Xiaomi and Dell did. TMDS means the HDMI 2.0 row, whatever the version says.

The link also runs at its slower end. A 48 Gbps monitor on a card or cable that cannot do 48 Gbps gets the slower speed. HDMI.org pairs 48 Gbps with the Ultra High Speed cable.

Where this stops applying

Every figure is full RGB colour (4:4:4) at CVT reduced blanking v2, with the payload worked out from the encoding rate alone. Monitors ship their own timings, and a shorter blank moves the close cases, such as 1440p 360 Hz at 92% of 48 Gbps. DSC lifts every ceiling in the table. That is covered in the DSC article, which also notes HDMI 2.2. We left games consoles out, because we found no first-party statement of their HDMI link speeds. The worked case is arithmetic from published figures, not a test of the monitor. For the same table on other ports, see DisplayPort 1.2 and USB-C. For what each refresh step is worth once it runs, see the refresh rate guide.

Sources

• Texas Instruments, Migrating From HDMI2.0 to HDMI2.1, application note SLLA598, 2022 (FRL lanes and the six rate and lane settings).
• TFTCentral, When HDMI 2.1 Isn't HDMI 2.1, December 13, 2021 (HDMI.org's statements, FRL and TMDS, the Xiaomi monitor).
• TFTCentral, HDMI 2.2 Explained, July 16, 2025 (16b/18b encoding, 88.8% efficiency).
• TFTCentral, Dell Alienware AW2725DF review, February 17, 2024 (TMDS HDMI port, 144 Hz over HDMI).
• Dell Community, AW2725DF, why HDMI 2.1 limited to 144hz@1440p?, March 3, 2024 (read via web.archive.org).
• HDMI.org, HDMI specification page (Ultra High Speed cable, up to 48 Gbps).
• MSI, MAG 271QPX QD-OLED datasheet and MPG 271QRX QD-OLED datasheet (HDMI 2.1, WQHD at 360 Hz).
• ViewSonic, XG273B-2K-OLED product page (1440p 360 Hz 10-bit RGB over HDMI 2.1).
• kevinlekiller, CVT 1.2 modeline calculator (reduced blanking v2 timings, the method for every mode here).