There is a distance scale on most maps of ME. Of course it will differ with the size of the map. On mine 2" is 300 miles. Measured somewhat inaccurately in straight lines, it was an estimated 385 mi. from Rivendell through Moria to Lorien. I don't know if that's even close to right, but that's what I got. According to the tale of years,it took the company 23 days (Dec. 25- Jan 17) to complete that leg of the journey, which I think is pretty good, considering.
From the western shore of forlindon to the eastern shore of the sea of Rhûn is roughly 1800 mi. It's also roughly 1800 mi from the havens of umbar to the northern most bit of the forodwaith shown on my map. Middle-earth is kind of a square.