24" vs. 27" 4K display – which is better for an external Retina Display?

Discussion in 'Mac Accessories' started by inkyoto, Jul 29, 2015.

  1. inkyoto, Jul 29, 2015
    Last edited: Jul 29, 2015

    inkyoto macrumors regular


    Oct 30, 2013
    Hey all, I'm looking to buy a 4K display for my MacBook Pro to run in Retina. As far as I see, there are basically two sets of options, 24" and 27", for 4K displays. I want a really clear display with crystal clear text, though, and I worry that the larger display will have pixels that are too large. Here's what the PPIs look like:

    • MacBook Pro Retina 15.4" — 220.42 ppi

    24" 4K
    • Dell 24" P2415Q — 183.58 ppi (83% of MBP)

    27–28" 4K
    • Dell 27" P2715Q — 163.18 ppi (74% of MBP)
    • Samsung 28" U28D590D — 157.35 ppi (71% of MBP)

    So, would it be a better idea to go for the 24" or the 27"? Will the difference between the two be large enough to notice? I like to run my MacBook Pro at true 2x, not scaled. If I do that on a 27", will text be too large, necessitating scaling? Does anyone own a 4K display that can speak to which one is preferable? Thanks!

    (Edit: I'm aware of the discussions going on in the Dell 4K display thread, but it's quite noisy and doesn't seem to focus around comparing the 24" vs. 27".)
  2. inkyoto thread starter macrumors regular


    Oct 30, 2013
    I've made a few more calculations to see how much bigger the 24" and the 27" would be:

    Assuming you could buy a 4K screen at 220ppi (same as MBP):
    dimensions = 17.4” x 9.8”
    diagonal = at 220.42ppi a 4K screen would run 17.41” by 9.79” = 20” diagonal
    area = 20” 4K @ 220.42ppi area = 170.44 in²

    24” 4K screen
    dimensions = 20.875” x 11.75”
    diagonal = 24”
    area = 245.28 in² = 43.9% more area than hypothetical perfect retina

    27” 4K screen
    dimensions = 23.5” x 13.25”
    diagonal = 27”
    area = 311.375 in² = 82% more area than hypothetical perfect retina

    So, the 24" has the same pixels as the hypothetical MBP Retina screen at 4K (at 220ppi) but in 43.9% more area, and the 27" in 82% more area. Here's a comparison of how 24" and 27" would compare to a hypothetical Retina screen at 4K (at 220ppi) which is 20":

  3. venom600 macrumors 6502a

    Mar 23, 2003
    Los Angeles, CA
    You're putting way too much thought into this man. I get it, you want the best display possible, but having seen 4k displays from 24-32", the truth is that in HiDPI mode (Retina mode), the OS does such a good job smoothing things out that you can't tell the difference. Don't worry about the size... worry about the screen quality. Most of the cheaper 27" displays are cheap TN panels that don't have good color accuracy. Try and find an IPS panel (like the 24" Dell) or, if you are feeling flush with cash, one of the 32" IGZO panels.

    Or, if you have one of the new 15" Macbook Pros with the Radeon, get a 5k display!
  4. Shamgar macrumors regular

    Jun 28, 2015
    If you want to run at 2x scaling, then get the 24". 1080p is a good resolution for that size, but is a poor use of a pricier 27" screen. The 27-28" models would be better used at 1440p equivalent.

    As for the PPI, that will depend on your typical viewing distance and eyesight. Is This Retina? is a website I just googled up that calculates the distance threshold for seeing individual pixels based on resolution and screen size. The numbers seem about right as a rough guide. A 28" 4k display has a retina threshold of about 22" between eyes and display. The 24" 4k has a threshold of 19" distant. Something like 28" is a typical distance, so any of those displays would be "retina class."
  5. inkyoto thread starter macrumors regular


    Oct 30, 2013
    Haha, yeah, I'm definitely overthinking this a bit, just looking to make the right purchase. I'm glad that the OS does the right scaling, though!

    Got it. Is 1440p a lot fuzzier at a normal distance, by any chance? Is it fuzzy like when you do the same "scaled" resolution on the MacBook Pro? Thanks for your help!
  6. Shamgar macrumors regular

    Jun 28, 2015
    I don't have a 4k, but I have been looking at getting the Dell P2715Q. The reports I've read do indicate that 1440p is "less sharp" to an extent comparable to the Retina Macbook Pro. I run my 15" at 1680x1050 equivalent and quite like it, so I'm sure I'd be happy at 1440p. However, if the reduction in sharpness is apparent and bothersome to you on an rMBP, I wouldn't expect anything better from a 4k display using a scaled resolution.
  7. bobbie424242 macrumors regular

    May 16, 2015
    I'm using the Dell 24" @ 1080p HiDpi and perfectly happy with it. The 24" is very compact and thanks to the higher dpi, it is totally fine being close to the monitor (which makes it looks bigger somehow).

    I never compared with the 27" @ 1080p or 1440p so cannot comment on that.
    My brief tests at 1440p incurred a noticeable performace loss using the 2014 rMBP with integrated graphics (the Iris Pro) only (I cannot comment on what perf would be using the dGPU of other models), especially in scrolling but not so much for animations. It's clear that the integrated GPU shows its limits at scaled resolutions other than 1080p and 2160p (the latter being native but unusuable for working). If the 27" is better used at 1440p, think about it, although you should get the opinion of someone else if your mac has a dGPU. It is also unclear if El Capitan will improve performance (observations above done on 10.10.4).

    These Dell monitors are both excellent and the best companions for retina quality on a big display.
    My dream would be a 16:10 version of these.
  8. inkyoto thread starter macrumors regular


    Oct 30, 2013
    Got it, that makes sense. Thanks for your help – I'm going to see how the 27" looks but default to the 24".

    Thanks for your input! I, too, wish for a 16:10 version of the displays, but we'll have to settle for 16:9 for now (at least until Apple comes out with a 4K Thunderbolt! C'mon Cupertino!) I'm really glad that the Dell monitors are top-knotch – it's incredible to be able to find quality 4K displays that use IPS at this price point. I do have a dGPU so I hope it does better on the scaled resolutions – not expecting much but hopefully it's usable.
  9. BomexM3 macrumors member

    Jan 4, 2014
    Are you planning on using the scaled resolutions or best for display setting??
  10. inkyoto thread starter macrumors regular


    Oct 30, 2013
    I'd prefer to use the best for display (exact 2x scaling), but I'm open to seeing how it looks scaled.
  11. pastrychef macrumors 601


    Sep 15, 2006
    New York City, NY
    I use a Dell P2715Q at 3200x1800 resolution and everything looks crystal clear to me. I did, however, turn off font smoothing in system preferences. This made a huge difference for me.

    Also, I recommend you try and have a look at the Samsung U28D590D before putting it in to consideration. I originally considered purchasing one when I was shopping for a 4K monitor and was extremely disappointed when I saw it first hand. In my opinion, the IPS panel used in my Dell is far superior to the TN panel used in the Samsung. This is especially true when viewing from an angle.
  12. Ray2 macrumors 6502a

    Jul 8, 2014
    I went from 24" to a very short life with a 27" and settled on a 25". Not all that different but the 25" resulted in a lot less moving my head to view the edges. Something to consider depending on the distance away from your display. Trying to maximize ppi tends to bring you closer to the display.

    I also forgot about 4k and just went with 2560.
  13. zhenya macrumors 603


    Jan 6, 2005
    If you are insistent on running 2x, get the 24". As stated, the 1920x1080 resolution you'll get at 2x is overly large on the 27".

    That said, I have the 27" Dell, and it's a fantastic monitor for the price. Remember that the larger the screen you use the further you will stand back from it, so the pixel density doesn't have to be directly on par. You will typically be much further from a 27" screen than you would sit from your laptop screen.
  14. Fishrrman macrumors P6


    Feb 20, 2009

    What you want depends on how good your eyesight is.

    For folks with "older eyes" (like me) or for those who are visually-impaired, the larger display is better, because text at any "designated size" (such as 12-point, 14-point, etc.) is a bit larger.
    In my case, I need text characters of a certain absolute size in order to resolve them. In other words, on a smaller (but retina) screen, small text would remain unreadable to me.

    Although I would think that with retina, even a 27" display will look crystal-clear.

    Looking at the 27" retina and non-retina iMacs side-by-side, even with my old vision, I can clearly see the retina screen is better.

    Why do people buy a 60" tv screen when they can do well with a 40" screen?
    After all, usually the resolution is the same.
    (Yes, I know super-high resolution tv is coming soon...)
  15. zhenya macrumors 603


    Jan 6, 2005
    Because a 60" TV will maintain the relative image size at a further seating distance, and as you sit further away, the effects of the lower dpi become less apparent. TV size should be based upon the size of your room.
  16. edanuff macrumors 6502

    Oct 30, 2008
    I did this same calculation and tried out several sizes of 4K monitors. The 24" 4K monitor at 2X scaling does in fact give you the truest Retina experience. My recommendation is that you buy a 27" monitor from somewhere with a return policy and see what the scaling looks like firsthand. It's going to be a matter of preference for you as to whether 2X on the 27" looks too big and whether the scaling artifacts with 1.5X are noticeable.
  17. robgendreau macrumors 68040

    Jul 13, 2008
    The ergonomics of retina matter a lot.

    You could defeat the whole purpose of your purchase if, in arranging things, you move the laptop back from your eyes (losing the benefit of retina, and essentially seeing smaller images since they're farther away). And to compound the problem you move the monitor too close, and see pixellation. Worst of both worlds. It can be trickier to arrange than you think, especially with the bigger monitor.

    I use a 5k next to a 2.5k, both at 27", and they are 16" and about 31" from my eyes, to get the best use out of both. You'd need to arrange the laptop and monitor in similar ways, using the calculator cited above, to get the best use out of both.
  18. dagamer34 macrumors 65816


    May 1, 2007
    Houston, TX
    I'd argue that 24" vs 27" only matters if you are also using your laptop screen at the same time, because then having a difference in relative size of items on other screens can be annoying depending on your sensibilities. If however you have the laptop screen closed, get whatever feels comfortable to you.
  19. keiran_harris macrumors newbie


    Jul 27, 2015

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