I’m just going to keep posting about this every few months because people keep getting “retina” wrong. According to this YouTube video that was recommended to me today, retina on desktop monitors is exactly 218ppi (pixels per inch). Now of course the iPhone 4, which was the first product with a display that got the "retina" catchphrase, had a 326ppi display, so obviously neither 218 nor 326 is a magic number.

What actually is "retina"

The basic idea of "retina" (which to be clear is a marketing term more than a scientific one) is that it is a display with pixels so small that someone using the screen at a typical viewing distance can't make out the individual pixels. But there isn't some magic pixels per inch value where a screen objectively achieves that status.

Let's get the essential thing out of the way: not everyone has perfect vision. If you don't have 20/20 vision, you would likely consider "retina" to be at a lower PPI than someone with perfect vision.

Another variable is distance. The iPhone was considered "retina" at a bit over 300ppi, but desktop monitors only require a bit over 200ppi. Meanwhile, the Apple Vision Pro's displays have 3,386ppi and while they're utterly amazing for 2025, it's also clear using one that there's room to improve display clarity on this product. The reason people consider 218ppi "retina" while another screen with pixels 15x narrower isn't "retina" is due to how close your eyes are to the screens in question. You likely sit a few feet from your computer monitor, your phone is usually closer to you in your hand, and the Vision Pro is strapped to your face where you can not escape…sorry, you are exceptionally close to the displays.

Retina is actually a measure of pixels per degree

So because "retina" is determined by a combination of pixels per inch and distance, we're actually talking about pixels per degree (PPD) of vision. Screens you hold close to your face need more pixel per inch to look sharp than those further away.

The Wikipedia page for Retina display is pretty good at explaining this:

When introducing the iPhone 4, Steve Jobs said the density of pixels needed for a Retina display is about 300 PPI (120 dot/cm) for a device held 10 to 12 inches (25 to 30 cm) from the eye.

Which means:

Based on Jobs' statement, the threshold for a Retina display is an angular pixel density of 52–63ppd. For example, holding a phone 11 in (28 cm) away, the value of 58ppd means that a tall skinny triangle emanating from the eye with a height equal to the viewing distance and a top angle of one degree will have a base on the device's screen that covers 58 pixels.

A quick jaunt over to my favorite pixels per degree calculator backs this up, showing the iPhone 4's 640 x 960 3.5-inch display having a cool 63ppd, and the benchmark for what "retina" means for years to come.

If you were curious, modern iPhones have upped the clarity since that original "retina" screen, with the latest iPhone 16 Pro having a 1206 x 2622 6.1-inch display, which works out to 159ppd, which is basically another doubling of resolution since the original "retina" screen. This alone should give you an indication that all of this is a measurement of gray areas, not some line in the sand where suddently pixels become invisible. Why go so hard on improving screens if you already couldn't see the pixels on the iPhone 4 display in 2010, right?

Onto desktop displays, and the reason we always get cranky at each other over this

Let's get to the part where I still know people will get mad at me. Apple's 27" Studio Display has a 5K resolution (5120 x 2880), which is 218 pixels per inch. But what's it's pixels per degree? Well ,that's where it gets tricky because people have different desk setups.

Remember that the original "retina" display had 63 pixels per degree of resolution.

With a 27" 5K monitor, you can get as close as 14 inches from the screen for it to remain "retina" and anything further back is gravy on top.

For comparison, a dirty, disgusting, "non-retina" 27" 4K display only gets that 63 pixels per degree rating at 20 inches from the display.

Then there are sickos like me who have a 32" 4K monitor, which is "retina" at 24 inches away.

If you use a monitor at a desk for your work or games or whatever, get a measuring tape out and measure how far away your eyes are from the screen. For me, the number seems to be around 28-30 inches depending on what I'm doing. For reference, I can easily stick my arm out in front of me and still have a few inches from my hand to my monitor. I'll freely admit that my display is less sharp than a 5K monitor and that I can certainly see the pixels when I put my head close to the screen. I'll also say that it's really hard to go backwards in screen tech once you're used to something better. If I'd been using a 27" 5K monitor for years, I'm sure this would look less good to my eyes because I was used to something crisper.

I'm not saying that an 8K version of my 32" monitor wouldn't be better (my poor GPU though), I'm just saying it clears a bar that works for my eyes at my desk setup, and I wish people would have more empathy for other use cases than this dogmatic "anything less than 5K at 27-inches is unacceptable for discerning Apple users,” idea. Besides, I spend half as much as a Studio Display and got 240Hz, variable refresh rate, real HDR, and OLED, so it's not like I'm suffering over here. 😛

That thing about UI size

The video brings this up as a feature, and I've heard others bring it up as well, and it's this idea that the macOS UI is meant to be displayed at a certain physical size, and Apple's monitors are designed to make the UI the same size whether you're looking at it on a 13" laptop or a 32" desktop monitor. To prove this, they show a Finder window moving from their laptop to their Studio Display and the size stays the same.

Once again, I won't argue the technicality, but I will push back on the idea that there is one true size for the UI. There is a default size, but many people have many reasons to change that to suit their needs. As with all parts of computer UI design, things are meant to be resizable because different people have different needs and preferences. Personally, I actually like that my UI is a bit bigger on my desktop display than it is on my laptop. I'm physically closer to my laptop when I'm using it, so the UI can be smaller without losing its legibility. Meanwhile, I'm sitting further from my display at my desk, so a larger UI looks pretty similar in size to me. This is extra helpful when I'm recording my podcast and I'm sitting about 6 feet from my screen and still need to be able to use it from that distance.

Anyway, all this is a very long way to say:

  1. Obviously, 5K is more crisp than 4K
  2. "Retina" is a fuzzy concept that's different for different people
  3. It's hard to go backwards once you're used to something
  4. Always remember to have empathy for those with different needs and requirements than you

Until next time I'm compelled the try and change a few more hearts and minds…

Just to add since it will likely come up, I too am sensitive to imperfect UI scaling, which is why I set my display to show me a perfectly pixel-doubled 1080p image. This completely eliminates the aliasing you see when upscaling 1440p output to 4k.