I have a mid-2015 MacBook Pro running High Sierra. I normally use it as a desktop computer in clamshell mode with an external monitor.

I just replaced my 24-inch external monitor with a 32-inch monitor. The new monitor is an Acer EB321HQU-B, which is supposed to support up to 2560x1440 resolution.

According to the technical specifications my Mac is supposed to support

full native resolution on the built-in display and up to 3840 by 2160 pixels on up to two external displays, both at millions of colors.


Support for 3840-by-2160 resolution at 30Hz

I have the new monitor connected via a Mini DisplayPort to HDMI adapter.

But the best I can get is 1920x1080, which is the same as my old monitor. In Display preferences, the only options I see in Scaled are 1600x900, 1080p, 1080i, and 720p, whether I select 60Hz or 30Hz. So I can't show any more on the screen, it's just all scaled up 33%.

Is there some way I can take advantage of the new monitor?


The problem is the cable you’re using to connect the monitor to the computer.

The easiest way to ensure that you have the full resolution is to use a standard mini-DisplayPort to DisplayPort cable and you should be able to use the full resolution without problems.

You can also use a mini-DisplayPort to DVI cable, but these are usually harder to come by in a standard home electronics store.

Last but not least, it might be possible to get the full resolution by using a better HDMI cable. You'll need one that supports HDMI 1.3 or 1.4 to support the 2560x1440 resolution.

  • Thanks. I went to Staples, they didn't have any Mini-DP to DP in stock, but they ordered one for me. Assuming it solves the problem I'll accept this answer. – Barmar Mar 17 '19 at 23:59
  • I probably won't be able to accept the answer for a couple of weeks; the cable may not arrive until Friday, and I'll be away on vacation. I'm just wondering if you think it will also address another issue I'm seeing: when I do screen sleep, the monitor backlight stays on. Will it be able to go completely black with DP? – Barmar Mar 19 '19 at 0:42
  • The cable came today, the result is beautiful. – Barmar Mar 20 '19 at 15:03
  • The issue with screen sleep is actually something else. It's ignoring the "Put the screen to sleep" setting in Energy Saver, and showing the screen saver, which is set to a black screen. I didn't have this problem with my previous VGA monitor. I'll open a new question. – Barmar Mar 20 '19 at 15:05
  • Sounds good with the cable :-) – jksoegaard Mar 20 '19 at 15:24

Why did you not use a Mini DisplayPort to DVI adapter? For example, this item.

A mini-DisplayPort actually has the DVI signals. Only the jack is smaller. The converter does not need to convert the signals. There are just wires connected between the smaller mini-DisplayPort pins and the larger DVI jack pins.

  • Because that's what the MicroCenter salesman sold me. – Barmar Mar 17 '19 at 22:06
  • The monitor came with an HDMI cable, so he sold me the adapter for it. – Barmar Mar 17 '19 at 22:07
  • Can I assume since you have a HDMI port, that there is also a DVI port, but no Display port (DP)? – David Anderson Mar 17 '19 at 22:20
  • @DavidAnderson I know the monitor - it has HDMI, DVI and DisplayPort as I wrote in my answer. – jksoegaard Mar 17 '19 at 22:23
  • Right, it has all those ports, but the only cable I have is HDMI. I've ordered a new cable. – Barmar Mar 18 '19 at 0:01

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