What was the total distance traveled by Lewis & Clark?

Answer 1

"When Clark arrived at the mouth of the Columbia River on November 16, 1805, he calculated that he had covered 4,142 miles from the mouth of the Missouri River. The National Park Service, which oversees the Lewis and Clark National Historic Trail, states that it is actually about 3,700 miles long."
But remember that they walked home, too. And the team divided to recross the Rockies coming back, so the expedition traveled at least 7,500 miles.

Answer 2

2151 miles approximately from St. Louis to the Pacific