The quick rule is to get a wide screen set with a diagonal size at minimum of 1.224 times that of
your old 4:3 analog standard definition set.
Enter a value in inches in any blue cell, then leave cell to recalculate entire bottom row.
The values in the yellow cells are 2.25 larger than the HD cells. That makes pixels
the same size as the SD pixels, giving a true comparison of screen sizes.
SD  HD calculator 


HD 16:9 (by pixel) 
Vert  Horz  Diag 




HD recommended size 
Vert  Horz  Diag 




I recommend a set 1.5 times taller that your existing SD(4:3) set.
This allows you a balance between a larger screen and a sharper image.
SD = Standard Definition
HD = High Definition
These height and width of images below are half sized so they will fit on your screen.
The actual pixel dimensions (resolution) of SD is 640x480 and HD is either 1920x1080,
which is used by CBS and NBC, or 1280x720 which is used by ABC and most cable and dish providers.
The High Definition resolutions were defined by the Advanced Television Standards Committee (ATSC)
in the 1990's and many TV stations have been broadcasting an HD signal since before 2000.
The width to height ratio of SD is 4:3 and HD is 16:9.
Hereafter I'll refer to Standard Resolution as 480 and I'll refer
to 1280x720 as 720 and 1920x1080 as 1080. Both 720 and 1080
have a wider screen than 480, so replacing an SD set becomes problematic as it won't fit
in the same space. If you choose a set the same width as your old SD set, you will
end up with a smaller screen, Exactly the opposite and wrong thing to do.
I recommend that in order to choose a new HD (wide) television, you measure the HEIGHT of your SD screen,
and choose an HD set at least that high. The table and calculator above can help you find the
diagonal measurment (that deceptive comparison tool the industry devised) that will ensure you
a pleasing HD viewing experience.
As you can see below, six Standrd Definition screens can fit in one 1920x1080 HD screen.
Here's an HD image (half sized to fit screen)
Here's a SD vertion (pillar boxed) upscaled to 1080. Note how fuzzy it is.
Here's an SD vertion (pillar boxed) upscaled to 1080 and improperly stretched to full width of screen.
Here's an SD vertion (pillar boxed) upscaled to 720. Note it is smaller and appearingly less fuzzy.
For those with large monitors, here are actual size versions of the four halfsized images above.
Here's an HD image (1920 x 1080)
Here's a SD vertion (pillar boxed) upscaled to 1080. Note how fuzzy it is.
Here's an SD vertion (pillar boxed) upscaled to 1080 and improperly stretched to full width of screen.
Here's an SD vertion (pillar boxed) upscaled to 720. Note it is smaller and appearingly less fuzzy.