What size HD widescreen monitor would “match” a 19" monitor?

I have two 19" Dell monitors with a 1280x1024 resolution. Because they are the exact same size, applications can span both monitors seamlessly. I'm considering adding a widescreen HD monitor that has 1920x1080 resolution, but that has the same size pixels as my current 19" monitor. That way, applications will still be able to span both monitors seamlessly.

What specifications would I need to look for in a widescreen monitor to make sure it "matches" my existing monitor?

I thought I would try to calculate the size of the pixels myself and go from there. I tried to solve the following system of equations to find out what size monitor might match, which came out to about 25.5"

``````(1920a)^2 + (1080a)^2 = b^2, (1280a)^2 + (1024a)^2 = 19^2
``````

However, I've looked around and don't know of any 25.5" monitors and the 19" measurement of my existing monitor is likely an approximation. Because of that, I'm not sure what to look for to make sure I have a matching 1920 x 1080 monitor.