Printing .stl file using ObJetPro 3D Printer
the best way is to install slicer on your pc and open the .stl file.
Most slicers will tell you the size of an object and there is an option to rescale resize.

Using Slic3r you will have object details in the corner


Using CURA you will have a detailed view in scale mode 


Also you can use online services CLICK