How to get all measurments on Eagle?
For board sizes and other mechanical locations, there are two ways of displaying the information. One way is using the dimension tool, found on the left side right above the ratsnest tool. You pick a starting point and an end point, and you can find distances that way. Sometimes this works well, especially for the width and length of the board as you can click near the center and it will grab the entire length. For cluttered or smaller things, it doesn't work out so well. 

The second way is to use the coordinates of the part you placed. This can be found by using the 'i' tool or by right clicking on the part and selecting properties. It will tell you the grid coordinate, and you can figure out distances from there; and also change the position to something more manageable usually (e.g. whole numbers).