Working with Roman Numerals

Excel includes a worksheet function that allows you to convert a number to Roman numerals. (Hmmm. Let's see... I was born in MCMLVI. Dang! I'm a classic!) The simplest way to use the Roman numerals is as follows:

=ROMAN(123)

All you need to do, obviously, is replace 123 with the number you want converted. You can use any number between 1 and 3999. (Romans apparently never worked with numbers outside this range.)

You can also, if desired, use a second argument to indicate how the resulting Roman numerals should be put together. The different arguments you can use are 0 through 4, with 0 being the default. An argument of 0 returns Roman numerals in the classic form, and 4 returns an extremely simplified Roman numeral. Values between 0 and 4 return progressively more simplified versions. The simplification of Roman numerals typically only comes into play when dealing with larger numbers. For instance, the following shows the various levels of simplification of the number 1999:

You should note that the ROMAN function returns a text value, and you therefore cannot use the result in any sort of calculation—as far as Excel is concerned, it is no longer a number.

Older versions of Excel (including Excel 2003) do not include a function to convert Roman numerals back to Arabic numbers. If you want to use a formulaic approach to do the conversion, you can try this:

=MATCH(A1,INDEX(ROMAN(ROW(INDIRECT("1:4000"))),0),0)

This presumes that the Roman numerals are in cell A1. If you prefer, you can create your own user-defined function to do the conversion to Arabic:

Public Function UnRoman(RomanNumber As String) As Integer
    Dim MySum As Integer
    Dim MyDeduct As Integer
    Dim MyWord As String
    Dim L As String
    Dim WordLength As Integer
    Dim i As Integer
    Dim MyArray() As Integer

    MySum = 0
    MyDeduct = 0
    MyWord = UCase(RomanNumber)
    WordLength = Len(MyWord)
    ReDim MyArray(WordLength + 1)

    For i = 1 To WordLength
        L = Mid(MyWord, i, 1)
        MyArray(i) = Switch(L = "I", 1, L = "V", 5, _
          L = "X", 10, L = "L", 50, L = "C", 100, _
          L = "D", 500, L = "M", 1000)
        MySum = MySum + MyArray(i)
    Next
    For i = 1 To WordLength - 1
        If MyArray(i) < MyArray(i + 1) Then
            MyDeduct = MyDeduct + MyArray(i)
        End If
    Next
    'Now deduct twice the value of the subtraction numbers
    UnRoman = MySum - 2 * MyDeduct
End Function

ExcelTips is your source for cost-effective Microsoft Excel training. This tip (1956) applies to Microsoft Excel 97, 2000, 2002, and 2003.