Thank-you for the update on the TypeCover 3 weight.
You are welcome.
I used a different screen aspect ratio calculator (which came out with different results), but if what you say is true then the 12.1" screen is indeed larger (though not "much larger"). Any maths experts here?
Going by skaertus' calculator the 13" MBA has a screen as much larger than the SP3's screen is larger than the 11" MBA.
If you take a look at the DisplayWars website (http://www.displaywars.com/11,6-inch-16x9-vs-12,1-inch-3x2), then the areas would be as follows:
11.6-inch MacBook Air: 57.5 square inches
12.1-inch Surface 3 Pro: 67.57 square inches
I am assuming the Surface Pro 3 has a 12.1-inch display (and not 12.0-inch as I previously thought). According to these calculations, the Surface Pro 3 has 17.5% more area in the screen than the 11.6-inch MacBook Air.