You can use this formula to convert the value 12'6"" to the numeric value
12.6 in another cell...
=--SUBSTITUTE(SUBSTITUTE(A1,"'","."),"""","")
or you can use this...
SUBSTITUTE(SUBSTITUTE(A1,"'","."),"""","")
directly in a calculation involving other numeric values (no double unary is
required under this circumstance). You don't show any spaces between the
foot-mark and the number of inches; however, if that could occur, then you
would need to remove it. That can be done by adding another SUBSTITUTE
function call...
=--SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(A1,"'","."),"""","")," ","")