4K monitor stuck at 30 Hz on a Mac
Updated
Short answer
Something between your Mac and the monitor can't carry 4K at 60 Hz, so macOS picks 30 Hz. 4K at 60 Hz with 8-bit colour needs about 12.54 Gbps. HDMI 1.4, found on many cheap USB-C hubs and adapters, carries 8.16 Gbps, which only fits 4K at 30 Hz (6.18 Gbps).
What each connection can carry
The figures are effective data rates, after encoding overhead. The requirements use standard reduced-blanking timing: 4K at 30 Hz needs 6.18 Gbps, at 60 Hz 12.54 Gbps, and at 60 Hz with 10-bit colour (HDR) 15.68 Gbps.
| Link | Carries | 4K 60 Hz, 8-bit | 4K 60 Hz, 10-bit |
|---|---|---|---|
| HDMI 1.4 | 8.16 Gbps | No | No |
| DisplayPort HBR2, 2 lanes | 8.64 Gbps | No | No |
| DisplayPort HBR3, 2 lanes | 12.96 Gbps | Yes | No |
| HDMI 2.0 | 14.40 Gbps | Yes | No |
| DisplayPort HBR2, 4 lanes | 17.28 Gbps | Yes | Yes |
| DisplayPort HBR3, 4 lanes | 25.92 Gbps | Yes | Yes |
| DisplayPort UHBR10, 4 lanes | 38.69 Gbps | Yes | Yes |
The usual causes
- A hub or adapter with HDMI 1.4. If the box says “4K 30 Hz”, or gives no refresh rate, assume HDMI 1.4. This is the most common cause.
- The monitor's USB-C port is sharing lanes with USB. Many monitors with USB-C have a setting such as “USB-C prioritisation: high data speed”. It gives two of the four DisplayPort lanes to USB 3. At HBR2 that leaves 8.64 Gbps: 30 Hz. Switch it to “high resolution” and you get all four lanes back.
- HDMI 2.0 with 10-bit colour. HDR at 4K 60 Hz needs 15.68 Gbps; HDMI 2.0 carries 14.4. macOS may drop to 30 Hz or reduce the colour format.
- An older USB-C link. A link running HBR2 on four lanes (17.28 Gbps) is fine for 4K 60 Hz, but not for 4K 120 Hz, which needs 25.82 Gbps.
- A DisplayLink dock. DisplayLink doesn't use these links at all; what it can do depends on its chip. See DisplayLink limits on a Mac.
How to fix it
- Check the refresh rate in System Settings → Displays: pick the monitor and look at Refresh rate. If 60 Hz isn't listed, the connection is the limit.
- Plug the monitor into the Mac directly. A USB-C to USB-C cable (if the monitor has USB-C) or a USB-C to DisplayPort cable can give four lanes of HBR3, 25.92 Gbps, on Apple silicon Macs when the monitor supports it (many monitors negotiate HBR2, 17.28 Gbps, which is still enough for 4K 60 Hz).
- If your Mac has HDMI, use it. MacBook Pro models with M2 Pro or later, the M2 Pro Mac mini and the M4 Mac mini have HDMI 2.1. M1 Pro and M1 Max MacBook Pro and the M1 and M2 Mac mini drive HDMI at up to 4K 60 Hz (HDMI 2.0), which is fine for 4K 60 Hz at 8-bit.
- If you need a hub, buy one whose HDMI port says “4K 60 Hz” and “HDMI 2.0” or newer, or one with a DisplayPort output.
- For HDR at 4K 60 Hz, use DisplayPort or USB-C, or HDMI 2.1.
Not sure what you have? The compatibility checker shows what to expect for your Mac and connection.