I don't worry whether it's in kilometers or miles as long as it's listed which one it is and the values are correct. I just think of it as Magic Numbers A and Magic Numbers B, because they're really just good for comparison to each other.
For those who don't know, 1 knot is 1 nautical mile per hour. The base game uses knots for speed and nautical miles for distance on the geoscape, and it uses km for distance in the interception window. With knots vs nautical miles, you're really just comparing aircraft speed to flight distance, or flight time, so you don't need to know how far a nautical mile is. Similarly, in the interception window, you're simply comparing one weapon's range with another weapon's range, so you don't need to know how long a kilometer is.