Or you could compare with the RAL chart and order from there, any paint factor uses these formulae and they are the only way that's truly universal.
I've scanned mine in at its native size so by clicking the image, it can open to the full size and you'll see every paint code there is on there. Most greys are in the 7s but if you order from your factor don't forget to add the flake if you're doing a metallic finish.