Cups and mugs

It took me some time to adjust to the imperial units as inches, gallons etc. as people use it here. This is not impossible! Many people complain about it, but it's doable! Instead of "a few meters away" you say "a few yards" and so on. I can kind of estimate how tall people are now and e.g.  "he's six feet" started meaning something to me. Temperatures are a lot harder to deal with, but I got the point that 30°F is kind of cold and 60-70°F is alright. 

BUT, I always thought that a cup means cup (volume measure, eight fluid ounces are one cup, 16 cups are one gallon). Thus, when I was cooking rice I took a coffee mug, filled it almost up and because the recipe said "one cup of rice goes with one cup of water" I added the same amount of water. Indeed, it wouldn't matter how large a cup is, if the ratio rice:water was 1:1, but it wasn't for some weird reason (maybe they assume that the same amount evaporates and the rice:water ratio is constant, but not actually 1:1?!). It said, if you have 2 cups of rice, take 1.75 cups of water etc. As I visited friends, they had a measuring cup (Messbecher) and I learned, that a cup is tiny! It's like a small tea cup. So my "cup" was about twice the actual cup, hups. However, my rice worked out fine ;-)