Note: I don't think these forumla's have been released so this is mostly just community speculation/native forumals.
Body armor and boots use the raw weight of the armor. gloves are x2 and helmet is x3. Ideally you would want your total armor to be less then this:
5 + (2 x [Weapon Master skill]) + ([Strength above 10]/2)
Otherwise, you take a penalty on wpf and move speed. I think its something like ~10 wpf for every 1 kg over, but I could be wrong on that.