Why does toggling HiDPI change my desktop size?

The HiDPI switch chooses an available display mode with the opposite HiDPI setting. If there is no matching mode at the same desktop size, refresh rate and color depth, it can select a different size instead. Switching back therefore does not necessarily restore the original resolution.

For a worked comparison, see HiDPI versus LoDPI at the same desktop size.

HiDPI and LoDPI are separate entries in the display’s mode list. Having a 1728 × 1117 HiDPI desktop, for example, does not mean a 1728 × 1117 LoDPI mode also exists. The screen’s physical pixel count and the desktop size are different quantities. See HiDPI.

To switch predictably, select the exact desired mode in Display Mode instead of relying on the toggle. For scripts, inspect the current list first:

betterdisplaycli get -name="Built-in Display" -displayModeList

Use a mode from that display’s current list. Specifying a resolution and HiDPI preference does not create a missing mode, and a nearest available match may be selected. The CLI examples explain mode selection.

If the size is absent, add a custom resolution or enable flexible scaling, apply the configuration and follow the requested activation steps. Flexible scaling requires Pro. These options can add useful HiDPI and LoDPI choices, but macOS and display limits still determine which modes become available. Recheck the list before relying on a pair of modes for testing or automation.