Hmmm, not sure if this is what you need, but assuming this input:
96"x42"x31"
This is column B (rounded up to nearest 100th of a foot)
=ROUNDUP(LEFT(A6,FIND(CHAR(34),A6)-1)/
12,2)&"'x"&ROUNDUP(MID(A6,FIND("x",A6)+1,FIND(CHAR(34),A6,FIND("x",A6))-
FIND("x",A6)-1)/
12,2)&"'x"&ROUNDUP(MID(A6,FIND("x",A6,FIND(CHAR(34),A6,FIND("x",A6)))
+1,2)/12,2)&"'"
This is column C, using the rounded values:
=ROUNDUP(LEFT(A6,FIND(CHAR(34),A6)-1)/
12,2)*ROUNDUP(MID(A6,FIND("x",A6)+1,FIND(CHAR(34),A6,FIND("x",A6))-
FIND("x",A6)-1)/
12,2)*ROUNDUP(MID(A6,FIND("x",A6,FIND(CHAR(34),A6,FIND("x",A6)))+1,2)/
12,2)&" cu ft"