1/9

1/9 may refer to:


 * 1/9 (number), a fraction (one ninth, $1/9$)
 * 1st Battalion, 9th Marines, an infantry battalion of the United States 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