Resolution Question

[H0MEY]

I was at the store as i'm in the market for a new laptop and I wanted to see what size screen and resolution I should get (I would like to run 2 browser windows on the smallest screen I can get and still be legible). But an interesting issue arose: I was testing how much screen size I could get on a given resolution so I opened up a spreadsheet to see how many rows and columns a given resolution would give. I noticed that 1920x1200 on the laptop only went to 49 and T while 1600x1200 on a PC went to 56 and V. Can someone explain how the bigger resolution gave less screen area?