Can USB-C do 4K at 120 Hz?
AnswerYes, if…
Yes, if the port carries DisplayPort 1.4 on all four lanes, or Thunderbolt 4 / USB4, and you use a full-featured USB-C cable. 8-bit 4K 120 Hz needs 25.82 Gbps, and DisplayPort 1.4 delivers 25.92. For 10-bit HDR at 4K 120 you need DSC, which most 4K 120 Hz monitors support. A dock or USB-C monitor that keeps USB 3 data running alongside the video has only half the lanes, and that tops out at 4K 60 Hz.
4K 120 Hz, 8-bit
| Link | Needs | Has | Result |
|---|---|---|---|
| USB-C DP 1.4 ×2 | 25.82 Gbps8.61 with DSC | 12.96 Gbps | With DSC |
| USB-C DP 1.4 ×4 | 25.82 Gbps | 25.92 Gbps | Fits |
| Thunderbolt 4 | 25.82 Gbps | 25.92 Gbps | Fits |
How the numbers are worked out
Reduced-blanking timing (VESA CVT-R2)
3840×2160 active → 3920 × 2287 total pixels per frame
3920 × 2287 × 120 Hz = 1075.80 MHz pixel clock
1075.80 MHz × 24.0 bits per pixel = 25.82 Gbps
8-bit colour, full RGB/4:4:4: 3 × 8 = 24.0 bits per pixel.
"Has" is the link's usable rate after line coding. DSC is modelled as up to 3:1 compression. Full method.
4K 120 Hz, 10-bit HDR
| Link | Needs | Has | Result |
|---|---|---|---|
| USB-C DP 1.4 ×2 | 32.27 Gbps10.76 with DSC | 12.96 Gbps | With DSC |
| USB-C DP 1.4 ×4 | 32.27 Gbps10.76 with DSC | 25.92 Gbps | With DSC |
| Thunderbolt 4 | 32.27 Gbps10.76 with DSC | 25.92 Gbps | With DSC |
What has to be true
- The port outputs video. Many USB-C ports don't. Look for a DisplayPort or Thunderbolt icon, or "DisplayPort Alt Mode" on the spec sheet.
- The port is DisplayPort 1.4 or newer. DisplayPort 1.2 over USB-C stops at 17.28 Gbps, which gives 4K 60 Hz but not 4K 120.
- All four lanes carry video, or DSC is on. USB-C monitors with built-in USB hubs often run 2-lane mode (12.96 Gbps). That still reaches 4K 120 Hz if both ends support DSC.
- The cable is full-featured. A USB 2.0 charging cable has no high-speed pairs at all. Any cable marked 10Gbps, 20Gbps, 40Gbps or Thunderbolt works for a 1 m run.
On a Mac or Windows laptop with Thunderbolt 4 or USB4, the DisplayPort signal is tunnelled. The same 25.92 Gbps-per-display ceiling applies, and DSC is supported on recent machines.
The standards involved
DisplayPort over USB-C (Alt Mode)
How most USB-C ports send video. The USB-C pairs are handed over to DisplayPort.
- data: USB 2.0 or USB 3 alongside
- video: DP 1.4 (or 2.1) over USB-C
- power: USB PD at the same time
DisplayPort 1.4
The current workhorse. 4K 120 Hz uncompressed, 4K 240 Hz and 8K with DSC.
- data: 32.4 Gbps
- video: 4K 120 Hz / 4K 240 Hz (DSC)
Thunderbolt 4
The same 40 Gbps as Thunderbolt 3, with the minimums raised so every port behaves the same.
- data: 40 Gbps (PCIe 32 Gbps)
- video: two 4K 60 Hz or one 8K
- power: up to 100 W (USB PD)
USB4 (20 and 40 Gbps)
Thunderbolt 3's protocol, opened up as a USB standard. Tunnels USB, DisplayPort and PCIe over one cable.
- data: 20 or 40 Gbps
- video: DisplayPort tunnelled
- power: USB PD required