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My iMac is detecting wrong display size

Just received a 21.5 inch iMac running El Capitan. I connected my AOC 21.5 inch external monitor and the display is way to blurry and large. I look directly to change the resolution and even after the (Option) + scaled radial trick that allows one to see more resolutions, when i pick the one that my display is natively (1920 x 1080) there's about 15% of my screen that is still black.


When I check the display tab in "about my mac" it shows the monitor as being 13.9 inches which it definitely is not. Please Help me 😟

iMac, OS X El Capitan (10.11.1)

Posted on Jan 16, 2016 3:21 AM

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Question marked as Best reply

Posted on Jan 17, 2016 8:57 AM

Hi blargwyir,

The resource below provides some options for configuring the resolution for your external display. You may need to refer to the manufacturer for additional guidance regarding best resolution for your model.

Get help with video issues on external displays connected to your Mac

Change your display resolution

  1. From the Apple menu, choose System Preferences.
  2. Click the Displays icon.
  3. Click Default for display. If you see more than one resolution listed, choose a resolution and refresh rate. If the display turns off when you change resolutions, press the escape key to undo the change.

    User uploaded file

If you can't change the resolution of your display because you can't see an image, restart your Mac in safe mode to reset the display resolution to defaults.

If starting in safe mode doesn't resolve the issue, reset your Mac's NVRAM and SMC to reset the video ports on your Mac to their defaults.

Take care,

1 reply
Question marked as Best reply

Jan 17, 2016 8:57 AM in response to blargwyir

Hi blargwyir,

The resource below provides some options for configuring the resolution for your external display. You may need to refer to the manufacturer for additional guidance regarding best resolution for your model.

Get help with video issues on external displays connected to your Mac

Change your display resolution

  1. From the Apple menu, choose System Preferences.
  2. Click the Displays icon.
  3. Click Default for display. If you see more than one resolution listed, choose a resolution and refresh rate. If the display turns off when you change resolutions, press the escape key to undo the change.

    User uploaded file

If you can't change the resolution of your display because you can't see an image, restart your Mac in safe mode to reset the display resolution to defaults.

If starting in safe mode doesn't resolve the issue, reset your Mac's NVRAM and SMC to reset the video ports on your Mac to their defaults.

Take care,

My iMac is detecting wrong display size

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