First off Model Info >> Change Units to cm rather than mm... Everything is always made the correct size whatever the units you are using... However, you've made everything in mm thinking them to be cm, so you have made something 100[mm] thinking it was 100[cm] - i.e. 10 times too small. There are 2 ways to rescale everything... Method one: 'select all' to highlight everything in the model [check nothing is off/hidden/locked etc] and then use scale about a diagonal corner pair of handles x10. Everything should now be x10 bigger and therefore the sizes you originally expected. Since you now have you model units in cm anything you make from now on will be the correct size when entered [in cm]... The other way you can rescale the whole model is this... Use the tape measure tool, pick a vertex point and stretch the tool cursor out say 100, now immediately type 1000 and a dialog pops up asking if you want to scale the model, if you say yes the whole model is scaled by 10 - every 100 dimension is now 1000.... mm have become cm...