The smoot /ˈsmuːt/ is a nonstandard, humorous unit of length created as part of an MIT fraternity pledge to Lambda Chi Alpha by Oliver R. Smoot, who in October 1958 lay down repeatedly on the Harvard Bridge between Boston and Cambridge, Massachusetts, so that his fraternity brothers could use his height to measure the length of the bridge.

[2][3] Over the years the "±" portion and "ε" spelling have been left out in many citations, including some markings at the site itself, but the "±" is recorded on a 50th-anniversary plaque at the end of the bridge.

[4]Oliver R. Smoot was selected by his Lambda Chi Alpha fraternity pledgemaster because he was deemed shortest—which made measuring the bridge the most labor-intensive—and he was the "most scientifically named.

Public knowledge and interest in the story began when Holiday investigated the marks on the bridge years later, and published an interview with Smoot.

[10] On May 7, 2016, Smoot served as grand marshal of the alumni parade across the bridge, celebrating the 100th anniversary of MIT's move from Boston to Cambridge.