How to Set Custom Resolutions for External Displays in Mac OS X

Whether you use Mojave or Catalina, Mac OS X usually handles display resolution and scaling quite well automatically. Still, those using external displays (particularly third-party displays) may wish to select their resolution manually. Here’s how you can override OS X’s automatic and limited suggestions and choose any supported resolution for your external monitor.

How to Set Custom Resolutions for External Displays in Mac OS X
  1. To change the resolution of your Mac’s display, head to System Preferences > Displays. If you have more than one screen connected to your Mac, a new Display Preferences window will appear for each one. Select the window residing on the display you wish to modify.
  2. By default, in recent versions of OS X, you’ll see a “default” recommended resolution for your external display. If you prefer a different screen size, OS X gives you four other options. The exact resolutions will vary depending on the specifications of your external display. Click on “Scaled” to view the display choices.

As referenced above, the external monitor connected to the Mac in the screenshots is a Phillips FTV HDTV, with a native resolution of 1080p. An actual PC monitor usually displays a “Looks like #### x ####” resolution underneath the TV image in the options window.

On the Phillips HDTV, OS X suggests a “default” resolution of a Retina-scaled 1080p equivalent, and we have the choice to set other resolutions (“scaled”) including 1280 x 768, 720P, 1080i, and 1080p.

While adequate for the majority of users, these five resolution choices (default and scaled) are missing several “in-between” display options, as well as “low resolution” modes, such as a true 2560×1440 that must be upscaled by the monitor and may be necessary for testing or software compatibility purposes. Thankfully, these resolutions are still accessible, and here’s how to access them.

  1. Press and hold the Option key on your keyboard, and then click the “Scaled” option again.
  2. Once you’ve found your desired resolution, click its entry in the list to switch your display.
  3. If you like a particular setting that fills the screen but cuts off the edges, slide the “Underscan:” slider until it properly fits your display area. The Phillips TV above required this step because the top and bottom areas were not viewable.

When using the above steps, the row of five recommended resolutions gets replaced by a complete list of ALL supported resolutions. Those using a 4K display can also click “Show low-resolution modes” to access the aforementioned low-rez options that will get upscaled via the device. If your Mac is connected to an HDTV, this list may also include alternate refresh rates and display modes if supported by the hardware. Everything you see is based on the TV or monitor model.

mac os x system preferences custom resolution

Mac OS X’s cool thing is the previews you get when choosing a resolution using the “Built-in Retina display” option, which is found under the “Optimize for:” section.

When you hover over the resolution thumbnails within the scaled settings, the system lets you see what a window will look like under that particular setting.

While your resolution choices will survive reboots, the “all compatible” resolution list described above isn’t always visible. OS X will revert to the default view after you close and reopen System Preferences. Just remember to click “Scaled” while holding the Option key, and you’ll see all compatible resolutions again.

6 thoughts on “How to Set Custom Resolutions for External Displays in Mac OS X”

kevin says:
thank you
steve says:
Thanks for the info!

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