1/9 may refer to:
1/9 (number), a fraction (one ninth, ) 1st Battalion, 9th Marines, an infantry battalion of the US Marine Corps January 9 or September 1, depending on date format "Breaker 1/9", a song by Common Former 1 (New York City Subway service) and 9 (New York City Subway service), which shared the same route U.S. Route 1/9, in New Jersey
See also 9/1 (disambiguation) 1-9 (disambiguation)