2×4 or two by four may refer to:

• ²
  ₄, a time signature in music
• 2×4 (Guadalcanal Diary album), 1987
• 2×4 (Einstürzende Neubauten album), 1984
• 2×4 (Malachi Favors and Tatsu Aoki album), 1999
• Two by Four, 1989 album by Marc Johnson
• "2×4", a 1996 song by Metallica from their album Load
• "2×4", a 1995 song by Blind Melon from their album Soup
• "2×4", a 1984 song by The Fall from their album The Wonderful and Frightening World Of...
• "2×4", a 1988 song by The U-Men from their album Step on a Bug

• 2by4 or 2x4, a 1998 American drama film
• 2 inch × 4 inch profile dimensional lumber
• 2×4 Roller Derby, a women's roller derby league in Argentina
• Jonny 2×4, a character on the cartoon Ed, Edd n Eddy

• 4x2 (disambiguation)