The cheese slope is 1x1, so 20LDU x 20LDU. Just looking at the LDraw code you posted, it looks like its 16 LDU tall. (I see Y values from 0 to -16.)
The approximate answer in the real world is that one LDraw Unit is equal to 0.4mm, so the cheese slope would be 8x8x6.4 (mm). The exact answer is much more complicated, so you should see this here:
http://www.lugnet.com/~330/FAQ/Build/dimensions
The approximate answer in the real world is that one LDraw Unit is equal to 0.4mm, so the cheese slope would be 8x8x6.4 (mm). The exact answer is much more complicated, so you should see this here:
http://www.lugnet.com/~330/FAQ/Build/dimensions