Click on Print in the Home tab.
In the first drop down of the Print dialog, choose "Fit to Scale"
Next, choose your scale. By default, the scale your diagram was drawn with will be selected. You'll notice that the paper size is not something you can change. To preserve that scale you will need to have access to paper that size. If you need to print to a specific paper size, you may need to change your scale. You can do so in the drop down for scale in the upper right of the dialog.
After you click "Continue," your diagram will be exported to a pdf.
When you print from your pdf viewing program, make sure that it is scaled to 100% or printing to Actual Size.
If printing from Chrome, uncheck the box that says “Fit to Page:”
If printing from Adobe Reader, make sure to select the “Actual Size” option: