Warhammer/40k is an english game and all measurements are taken in imperial
I work in metric 95% of the time but once in a while I have to convert an imperial drawing to metric, this is why I know most of the major imperial sizes as a metric conversion. On an odd note imperial micrometers confuse the f**k out of me where as Im fine with a metric one - I can read them, it just takes me twice as long to be certain Im reading the measurement I think Im reading
Centimeters are the devil spawn and should be illegal :D