How do you all convert between Miles, Nautical Miles and KM? I can do between KM and NM quite good but miles I'm not used to at all (being Swedish I never use them, so I need a quick formula to use to convert to and from miles).
I also never use miles. In Portugal we use kilometres. I really don't think there's any quick formula... You just need to know how to convert between units and do them as quickly as possible in your head. Nautical miles to miles are really easy because 1 nm = 1.15 miles, so if you want (for example) to know many miles are 400 nautical miles, you just need to calculate 15% of 400 and add the result to 400. In this case the result would be 460 miles.
Similarly, 1 mile = 1.6 km, so if you need to convert X miles to km, just calculate 60% of X and add the result to X. At least this is how I do it. I find it easier than doing X * 1.6 in my head.