Word is not drawing software and I think that you are dragging a circle to the size you want by using the horizontal and vertical rulers. This does not accurately define the circle size and I do not think there is an answer, using Word, except trial and error to get your printer to print out the size you want.

You would need CAD drawing software to draw objects and print them accurately because CAD software prompts you to type-in the circle radius or diameter and will print out that size accurately if printed at 1 to 1 scale.

I use professional software, AutoCAD, for drawing but there are many free CAD packages out there if you feel up to learning a new skill. Just search for "Free CAD software" on the internet.