How do you figure out the ppi (pixels per inch)?

Discussion in 'MacBook Pro' started by Luba, Apr 21, 2010.

  1. Luba macrumors 6502a

    Luba

    Joined:
    Apr 22, 2009
    #1
    I'v read that the 17" has 133 ppi, and the 15" high res has 128 ppi, but how is that figured out? I'd like to do the math for the 24" Apple Cinema Display. Thanks. :)
     
  2. sammich macrumors 601

    sammich

    Joined:
    Sep 26, 2006
    Location:
    Sarcasmville.
    #2
    Diagonal number of pixels: use Pythagoras:

    Code:
    sqrt((width^2)+(height^2))/diagonal length
    The ACD 24": (1920^2 + 1200^2)/24 = 94.3 dpi
     
  3. Chundles macrumors G4

    Chundles

    Joined:
    Jul 4, 2005
    #4
    Number of Pixels/Number of Inches

    Pretty straight forward maths.
     
  4. striatedglutes macrumors 6502

    Joined:
    Feb 22, 2009
    Location:
    USA
    #5
  5. ethical macrumors 68000

    Joined:
    Dec 22, 2007
    #6
    This OP ^^
     
  6. sammich macrumors 601

    sammich

    Joined:
    Sep 26, 2006
    Location:
    Sarcasmville.
    #7
    Damn, I hoped no one would notice that :( Was too busy adding the ACD calc
     
  7. ethical macrumors 68000

    Joined:
    Dec 22, 2007
    #8
    haha sorry :p

    i'll edit my post to save you :D
     
  8. Luba thread starter macrumors 6502a

    Luba

    Joined:
    Apr 22, 2009
  9. jiE macrumors regular

    Joined:
    Sep 1, 2007
    #10
    Well... Not this way. The number of inches is a measure of the diagonal length of the screen, and not (if this formular would be correct) an area of the screen.
     
  10. wandrer2 macrumors member

    Joined:
    Feb 9, 2010
    #11
    Also, just using the number of inches as specified by Apple is a bit inaccurate.

    Measure the width of the screen in inches = w
    Count the horizontal number of pixels = p

    ppi = p/w
     
  11. rodrigopolo macrumors newbie

    Joined:
    Sep 1, 2013
    #12
    JavaScript:
    Code:
    var width = 1920;
    var height = 1080;
    var diagonal_inches = 24;
    // result:
    Math.sqrt((Math.pow(width,2)+Math.pow(height,2)))/diagonal_inches
    
     

Share This Page