23. LCD Resolutions and Ratios (Part 2)

by orev
From Notebook Review


When you're looking for a laptop (or any type of screen), one of the things you should look at is the screen resolution. Some people care more about the size of the screen, but to me, it's both the size and the resolution that are important. The more pixels on the screen, the more stuff you can see at once.

While shopping recently for a laptop, I kept coming back to the question of: "Will the display resolution at this screen size be too big or small for me to read comfortably?" My current monitor has a nice size, and I wanted to be able to compare my monitor with the laptops out there. Of course, I can't take my monitor everywhere to compare.

This led me to the idea of looking at the DPI, or "Dots Per Inch". DPI measures how many dots (pixels) there are in 1 inch across or down on the screen. Because this measurement is specifically tied to a physical measurement, you can be sure that no matter what the resolution of the screen is, the DPI will tell you exactly how it will look.

I calculated the DPI for many common screen sizes at common resolutions, allowing a very direct comparison of DPI for these different screens. Here are the charts, broken down by aspect ratio (and you thought that learning the pythagorean theorum and all about sin/cos/tangents was useless!):

Widescreen Format (16:10) Display DPI Resolution

Diagonal (inches)	2560x1600 (WQXGA)	1920x1200 (WUXGA)	1680x1050 (WSXGA+)	1440x900 (WXGA+)	1280x800 (WXGA)
12.1	250x249	187x187	164x164	140x140	125x125
14.1	214x214	161x160	141x140	120x120	107x107
15	201x201	151x151	132x132	113x113	101x101
15.4	196x196	147x147	129x128	110x110	98x98
17	178x177	133x133	117x116	100x100	89x89
19	159x159	119x119	104x104	89x89	79x79
20	151x151	113x113	99x99	85x85	76x75
22	137x137	103x103	90x90	77x77	69x69
24	126x126	94x94	83x82	71x71	63x63
27	112x112	84x84	73x73	63x63	56x56
30	101x101	76x75	66x66	57x57	50x50

Standard Format (4:3) Display DPI Resolution

Diagonal (inches)	1600x1200 (UXGA)	1400x1050 (SXGA+)	1280x960	1024x768 (XGA)
12.1	165x165	145x145	132x132	106x106
14.1	142x142	124x124	113x114	91x91
15	133x133	117x117	107x107	85x85
17	118x118	103x103	94x94	75x75
19	105x105	92x92	84x84	67x67
20	100x100	87x88	80x80	64x64

SXGA (5:4) Display DPI Resolution

Diagonal (inches)	1280x1024 (SXGA)
12.1	135x135
14.1	116x116
15	109x109
17	96x96
19	86x86
20	82x82

Some of those size/resolution combinations don't exist (you'll probably never be able to get a 12.1" screen with a resolution of 2560x1600).

OK, how do you use these charts?

1. Figure out the resolution and size of your current display. To find the size of your display, take out a ruler and measure diagonally from corner to corner. To find the resolution, right-click on your desktop, choose Properties, then go to the settings tab. You will see a slider with the "screen resolution" listed.
2. Look up your monitor on the chart. For example: if you have a standard (4:3) format 17" display, with a resolution of 1400x1050, then your DPI is 103x103.
3. Now you can look at other DPI numbers in the chart and see what else matches up to your monitor.

One thing that many people worry about is if "things will be too small" on the monitor. It's true that the higher the resolution and DPI (bigger numbers), the smaller pictures and fonts will be on the screen. However, you can adjust the font settings to compensate for this on the Display control panel, using "Large fonts", or you can specify what DPI you have. This can make some of the Windows UI look out of proportion, though I hear that in Vista this should not happen. The advantage of doing this is that you will see much better resolution with photos, and fonts will also display more clearly (kind of like using cleartype). Many programs (like MS Office, Firefox) also have a "zoom" feature, that lets you make the fonts look bigger on the screen without changing how big they will be when printed.

Some notes on DPI:

• Bigger numbers mean smaller letters on the screen.
• Windows generally assumes you have a 96dpi display, no matter what you ACTUALLY have. At the moment, it's not possible (AFAIK) for Windows to automatically know what the actual DPI is without you telling it.
• I'm not sure how much this relates to DPI settings in Photoshop or other programs like that
• You can compare this to printed paper too. As far as I know, printed material is usually around 300 dpi.