If you're on a text only browser then you don't get much choice about the width...

Ruler in Pixels

2560 x 1440 (WQHD) ruler image
See LCD monitors in products

Browser Window Sizes

This is old data for Netscape Navigator 4 (NN4) and Internet explorer 5 (IE5)
  A maximized window on a VGA screen eliminates the border and
can display maximum of 610x295 pixels (770x415 w/ SVGA) with a
scroll bar on the right but not on the bottom. Height of the
display area can be increased to 385 by eliminating the:
                        NN4        IE5
   Title & border       20          23 
   Menu  bar            22          25
   Navigation tool bar  43*\        41*\ 65
   location tool bar    23*}  89    24*/ 
   personal tool bar    23*/
   Margin & border       8          20
                        ___        ___
                       139         133
   Usable area         290         295
   Status bar           20          21*
   Border                5           5
   Windows Task Bar     26          26
                      ____         ___
      TOTAL (for VGA)  480         480
    * Can be eliminated

 Max eliminating all * 379         381

  The scroll bar is 15 pixels
If you select a large system font the maximum vertical space is reduced because the menu area is larger.
A background needs to be 640 char. wide because it includes the margins.

Display Resolution

See Video Resolution Page.

* Viewable area is typically less than the nominal size (measured diagionally).
Resolutions of 100 pixels/inch or higher are difficult to read on a CRT, however the clarity of flat panel displays make them usable at higher resolutions.
See PC, Video & Multimedia at TDC
VGA - Video graphics array
SVGA - Super VGA
EVGA - Enhanced VGA - 1024x768.
XGA - Extended Graphics Array
SXGA - Super XGA
HDTV - High-Definition TV 1920 x 1080
QCIF - Quarter Common Interchange Format (H.263)

            Monitor Size
  e.g.   Nominal   Viewable Area
           13"       12.6
           15"      13.5-13.8"
           17"        15.7"
15" and 17" monitors from the same manufacturer usually support the
same resolution (usually EVGA or 1280x1024 maximum); The 17" screen
is just more readable.
See monitor specs at Compaq, NEC .

Resolution depends on the capability of the monitor, video card and video driver.
You can change the resolution for a given card and monitor by selecting a
different driver.

Pixel Density (PPI - Pixels/inch) usually ranges between 72 and 100
depending on the monitor size and resolution selected.
With Windows 3.1 a pixel density of 95 PPI results in a life size document.
i.e. the size on the screen matches the printed size. 72 PPI produces a
real size document on a Macintosh.

Small mobile phone page 320x480