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On my MacBook Pro, the System Report says that the resolution is "2560 x 1600 Retina". But when I use the Free Ruler app, it says that 1280 x 800. That's with resolutions set to "Default for Display" in the system display settings.

When the display setting is "Scaled" and "More Space", Free Ruler measures it as 1680 x 1050.

I struggle to understand what I see as a discreptancy and don’t understand "scaled resolution".

How do I get the screen to operate at the resolution claimed?

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  • You might get more resolution options from macOS Settings -> Displays if you click "Advanced...", and then enable "Show resolutions as list".
    – Bruce Van Allen
    Commented Oct 16, 2023 at 18:34
  • @BruceVanAllen, I'm on v 12.6.6 macos. And I don't see "Advanced..." anything . What version are you on?
    – Earnest Frankly
    Commented Oct 20, 2023 at 9:23
  • Ventura, 13.6 - and I don't recall seeing that "Advanced" option in previous versions, although I hadn't looked for it until your question got me curious. But I've never had the experience of being unable to use a Mac's display at its highest resolution, either. I assume you've poked through FreeRuler's docs to make sure you're getting correct readings?
    – Bruce Van Allen
    Commented Oct 20, 2023 at 16:01

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Your MacBook Pro has tiny pixels. Half the size of many 'normal' displays. As a result, an object that is 12 pixels wide would look half the size of a standard display.

So the solution is to make everything twice the size!

Where a 'normal' display would use 1 pixel, your display can use a 2x2 pixel square. But of course those 4 pixels can be different colors, and so your display has greater sharpness and detail for the same 'effective' size.

Your MBP has 2560 x 1600 pixels. But, at a 2x scaling, that's 1280 x 800. It's displaying everything at the size of a 1280 x 800 display, but using twice as many pixels to do so. (Well, ok, 4 times.)

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  • So the object is first scaled up by 2x2. So new pixels have to be filled in with extrapalated colors, right? Doesn't scaling up like this make the image appear more blurry?
    – Earnest Frankly
    Commented Oct 20, 2023 at 9:28
  • @ErnestFrankly No: the object appears more sharply. It's the same as zooming in. They are only extrapolated for bitmap data with no more detail. (E.g. you're already showing 1 screen pixel for 1 image data pixel. Vector graphics will scale to any size without loss of detail. Here's Steve Jobs explaining it: youtube.com/watch?v=Hq8j5vsqCCo
    – benwiggy
    Commented Oct 20, 2023 at 10:55
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One of the primary purposes of having a display with higher resolution is so that non-rectilinear shapes and edges will look smoother. You may recall "ancient" low-resolution displays where a rectangle looks fine, but the sides of a triangle or a circle would show "jaggys".

By "reporting" the display size as 1280x800, objects & fonts will be the size you expect to see (and are readable!). The display chip handles the interpolation/smoothing of the edges so that your eye discerns smoother curves than one might see on a "native" 1280x800 display.

As Bruce Van Allen commented, showing as a list, and then enabling to show all possible resolutions, will allow you to try the effects of different settings.

Why all the different possible resolutions? For one use-case, when mirroring a screen of a different native size and resolution the higher native resolutions of the MacBook lets it more accurately "mirror" the resolution of a screen with a different aspect ratio and resolution.

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