USB-C max refresh rate: can USB-C do 1440p 240 Hz?

Yes, but only on a USB-C port that runs DisplayPort on all four lanes at HBR3, and only at 8-bit colour. That link carries 25.92 Gbps of picture, and 1440p 240 Hz needs 24.62. Many USB-C setups use two lanes instead. Two HBR3 lanes stop at about 133 Hz at 1440p, so they miss even 144 Hz. Two HBR2 lanes stop at about 90 Hz.

What DisplayPort Alt Mode is, and what limits it

DisplayPort Alt Mode (alternate mode) lets a USB-C port send a real DisplayPort signal down some of its wires. Nothing is converted. A USB-C cable has four high-speed lanes, which are separate data paths side by side. In Alt Mode, the port gives two or four of them to DisplayPort.

VESA's 2019 USB DevDays presentation shows both layouts. With two lanes, the cable uses "two high-speed lanes each for DisplayPort and USB 3.2". VESA calls that "Ideal for docking stations, or for displays or TVs that include USB 3.2 functions". With four lanes, DisplayPort gets every high-speed lane, and only USB 2.0 is left for data. VESA's own note is plain: "2 Lane configuration is common for USB-C DP Alt Mode".

The second limit is the link rate, the speed of each lane. VESA's table gives HBR2 (High Bit Rate 2) at 5.4 Gbps per lane, from DisplayPort 1.2. HBR3 is 8.1 Gbps, from DisplayPort 1.3 and 1.4. Two bits in every ten are encoding overhead, so VESA multiplies by 0.8. Lane count times rate gives four payloads, the rate left for the picture:

A mode needs its pixel clock times 24 bits (8-bit colour) or 30 bits (10-bit). The pixel clock counts visible pixels plus blanking, the unseen gap around each line and frame.

Top refresh rate for each USB-C setup

We used 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. We stepped the refresh up one hertz at a time until the mode no longer fit.

The table agrees with VESA's own examples. VESA says two HBR2 lanes give "Two 1080p displays, or one 4k@30Hz". 4K tops out at 41 Hz there, so 30 Hz is the step that fits. Two HBR3 lanes give 4K at 60 Hz, and the table tops out at 61. Four HBR3 lanes give 5K at 60 Hz, a mode that needs 22.18 Gbps.

Some common modes, against each setup:

• 1440p 240 Hz needs 24.62 Gbps at 8-bit. Only four HBR3 lanes carry it, with 5% to spare. At 10-bit it needs 30.77, which no setup carries without compression.
• 1440p 165 Hz needs 16.30 Gbps. It fits four lanes at either rate, and no two-lane setup.
• 1440p 144 Hz needs 14.08 Gbps. Two HBR3 lanes carry 12.96, so it misses by about 9%.
• 3440 x 1440 at 144 Hz needs 18.77 Gbps. Only four HBR3 lanes carry it.

A monitor maker prints the same numbers

Dell's user's guide for the G3223D, a 1440p 165 Hz monitor, has a USB-C Prioritization setting. The default is "High Resolution 4 Lanes" (HBR3). Dell says it supports 2560 x 1440 at 165 Hz with 10-bit colour, and "USB performance will be reduced to USB 2.0". The other choice is "High Data Speed 2 Lanes".

Dell's table for that two-lane mode heads its columns 12.96 Gbps (HBR3) and 8.64 Gbps (HBR2), the same payloads as above. It marks 1440p at 120 Hz as working at 8-bit on two HBR3 lanes, and 1440p at 144 and 165 Hz as not working. It marks 1080p 144 Hz as working at 8-bit on two HBR2 lanes, but not at 10-bit. All twelve rows match our arithmetic.

Worked case: a 144 Hz ultrawide on a laptop's USB-C port

In an Acer community thread from January 2022, an owner of an XZ342CK, a 3440 x 1440 monitor rated for 144 Hz, could not pass 60 Hz. They used a USB-C to DisplayPort cable from a Dell Inspiron 5570 with Intel UHD 620 graphics. A custom resolution got them to 92 Hz, and "It wouldn't go any higher". Here is how the numbers read.

At 144 Hz the mode needs 18.77 Gbps at 8-bit. That is more than any HBR2 setup carries, and more than two HBR3 lanes. Only four HBR3 lanes fit it. So unless the port runs four HBR3 lanes, 144 Hz was never on the table.

Now take the 92 Hz they did reach. Even the visible pixels alone, with no blanking at all, come to 10.94 Gbps at 8-bit. Two HBR2 lanes carry 8.64. So that port was not running two HBR2 lanes. At four HBR2 lanes, the arithmetic top for this monitor is 133 Hz at 8-bit and 107 Hz at 10-bit. The thread does not say which lanes or rate the laptop used, so we leave that open.

The same poster got 100 Hz through a USB-C to HDMI adapter. VESA says those adapters "support up to HDMI 2.0b", and HDMI 2.0 tops out at 112 Hz at 3440 x 1440. An adapter adds its own limit on top of the port's.

How to tell what your port does

• The icon beside the port. Plugable's guide says "DisplayPort Alt Mode may be marked with a 'DP' icon", and "Thunderbolt ports may have a lightning bolt symbol". The word is "may", so read the spec sheet as well.
• The laptop's spec sheet. Plugable says to search the manual for "DisplayPort Alt Mode". If it names a DisplayPort version, VESA's table helps: HBR2 arrived with 1.2 and HBR3 with 1.3 and 1.4. A port listed as 1.2 tops out at HBR2.
• The monitor's USB hub. A monitor or dock that gives you fast USB ports over the same cable is the two-lane case VESA describes. On Dell's G3223D, "High Data Speed" picks two lanes. For a fast refresh, pick the high resolution option and accept USB 2.0 on the hub.
• The cable. VESA's USB-C to DisplayPort adapter cable carries four lanes of DisplayPort and no USB data, apart from a status function. A USB-C to HDMI adapter caps you at HDMI 2.0b.

Why "USB-C does 4K 60" and "USB-C caps at 60 Hz" are both heard

Both are true of some port. The phrase "DP 1.4 over USB-C" names the link rate but not the lane count. At HBR3 that covers 12.96 Gbps on two lanes and 25.92 on four, a factor of two. A spec sheet that promises 4K 60 Hz is met by two HBR3 lanes. The same port gives 1440p only 133 Hz in that setup, or 251 Hz with all four lanes. So check the lane count before the version number.

Compression changes this only if both ends support it. VESA's table gives two HBR3 lanes 5K at 60 Hz with DSC (Display Stream Compression). 1440p 240 Hz on two HBR3 lanes would need about 1.9:1. That is under the 3:1 VESA gives for DSC, as our DSC article explains. VESA lists DSC as a DisplayPort 1.4 feature, so an HBR2 port has none.

Where this stops applying

Every figure is full RGB colour (4:4:4) at CVT reduced blanking v2. Monitors ship their own timings, so close cases can go either way: 1440p 240 Hz on four HBR3 lanes, and 4K 120 Hz, which fits there by under 1%. A link runs at its slower end, and the graphics card only offers modes the monitor lists for that input. Thunderbolt and USB4 tunnel DisplayPort inside their own link. We did not fetch Intel or USB-IF documentation for them, so they are left out. The worked case is arithmetic on a forum thread, not a test of that laptop. For the cable side of a four-lane link, see which DisplayPort cable you need.

Sources

• VESA, DisplayPort Alt Mode over USB Type-C, USB DevDays 2019 (link rate table, payload formula, two-lane and four-lane pin assignments, example resolutions, DSC in DP 1.4, HDMI adapters up to 2.0b).
• Dell, G3223D monitor user's guide, USB-C Prioritization (copy hosted by ManualsLib).
• Plugable, How to Determine Your USB-C Port Video Capabilities, August 20, 2026.
• Acer Community, XZ342CK Refresh Rate Max'ed out at 60hz/3440x1440 using USB-C to DP, January 23, 2022.
• kevinlekiller, CVT 1.2 modeline calculator (reduced blanking v2 timings, run for every mode here).