Excel Feet To Inches
Update March 2017
Dan Ashby has an improved feetandinchesinexcel function available.
I have an Excel spreadsheet with a column of lengths in the format of 12' 6 7/8". How can I use Excel to convert this to decimal feet? I don't want to split the column into two parts. Then, how can I convert back to feet and inches in Excel?.
The custom function feet() shown below will take a text field in the format that you describe and convert it to decimal feet.
The custom function LenText will convert a decimal number of feet into a text field showing feet, inches, and fractional inches to the nearest 1/32".
To enter the custom function:
 Start the VB editor with altF11.
 Insert>Module.
 Insert>Procedure.
 Type feet as the name of the procedure and indicate it is a function.

Then, copy the following code:
Public Function feet(LenString As String) Dim FootSign As Integer Dim InchSign As Integer Dim SpaceSign As Integer Dim FracSign As Integer Dim InchString As String Dim Word2 As String ' Copyright 1999, 2005 MrExcel.com LenString = Application.WorksheetFunction.Trim(LenString) 'The find function returns an error when the target is not found 'Resume Next will prevent VBA from halting execution. On Error Resume Next FootSign = Application.WorksheetFunction.Find("'", LenString) If IsEmpty(FootSign) Or FootSign = 0 Then ' There are no feet in this expression feet = 0 FootSign = 0 Else feet = Val(Left(LenString, FootSign  1)) End If ' Handle the case where the foot sign is the last character If Len(LenString) = FootSign Then Exit Function ' Isolate the inch portion of the string InchString = Application.WorksheetFunction.Trim(Mid(LenString, FootSign + 1)) ' Strip off the inch sign, if there is one InchSign = Application.WorksheetFunction.Find("""", InchString) If Not IsEmpty(InchSign) Or InchSign = 0 Then InchString = Application.WorksheetFunction.Trim(Left(InchString, InchSign  1)) End If ' Do we have two words left, or one? SpaceSign = Application.WorksheetFunction.Find(" ", InchString) If IsEmpty(SpaceSign) Or SpaceSign = 0 Then ' There is only one word here. Is it inches or a fraction? FracSign = Application.WorksheetFunction.Find("/", InchString) If IsEmpty(FracSign) Or FracSign = 0 Then 'This word is inches feet = feet + Val(InchString) / 12 Else ' This word is fractional inches feet = feet + (Val(Left(InchString, FracSign  1)) / Val(Mid(InchString, FracSign + 1))) / 12 End If Else ' There are two words here. First word is inches feet = feet + Val(Left(InchString, SpaceSign  1)) / 12 ' Second word is fractional inches Word2 = Mid(InchString, SpaceSign + 1) FracSign = Application.WorksheetFunction.Find("/", Word2) If IsEmpty(FracSign) Or FracSign = 0 Then ' Return an error feet = "VALUE!" Else If FracSign = 0 Then feet = "VALUE!" Else feet = feet + (Val(Left(Word2, FracSign  1)) / Val(Mid(Word2, FracSign + 1))) / 12 End If End If End If End Function

Repeat for the function called LenText. Use this code:
Public Function LenText(FeetIn As Double) ' This function will change a decimal number of feet to the text string ' representation of feet, inches, and fractional inches. ' It will round the fractional inches to the nearest 1/x where x is the denominator. ' Copyright 1999 MrExcel.com Denominator = 32 ' must be 2, 4, 8, 16, 32, 64, 128, etc. NbrFeet = Fix(FeetIn) InchIn = (FeetIn  NbrFeet) * 12 NbrInches = Fix(InchIn) FracIn = (InchIn  NbrInches) * Denominator Numerator = Application.WorksheetFunction.Round(FracIn, 0) If Numerator = 0 Then FracText = "" ElseIf InchIn >= (11 + (31.4999999 / 32)) Then NbrFeet = NbrFeet + 1 NbrInches = 0 FracText = "" ElseIf Numerator = Denominator Then NbrInches = NbrInches + 1 FracText = "" Else Do ' If the numerator is even, divide both numerator and divisor by 2 If Numerator = Application.WorksheetFunction.Even(Numerator) Then Numerator = Numerator / 2 Denominator = Denominator / 2 Else FracText = " " & Numerator & "/" & Denominator Exit Do End If Loop End If LenText = NbrFeet & "' " & NbrInches & FracText & """" End Function
Column A shows the original text. Column B correctly converts to feet any values that contain feet, inches, and / or fractional inches.
Note that if you do not include the foot sign, the value is assumed to be inches. (row 12). If the fractional portion of the inches is not valid, Value! is returned (row 13).
Note: Thanks to Dale Richmond from Kansas City who provided an update in October 2007 to prevent an answer of 1 foot 12 inches when a number greater than 1.999 is passed to the function.