Function to convert column number to letter?

Solution 1:

This function returns the column letter for a given column number.

Function Col_Letter(lngCol As Long) As String
    Dim vArr
    vArr = Split(Cells(1, lngCol).Address(True, False), "$")
    Col_Letter = vArr(0)
End Function

testing code for column 100

Sub Test()
    MsgBox Col_Letter(100)
End Sub

Solution 2:

If you'd rather not use a range object:

Function ColumnLetter(ColumnNumber As Long) As String
    Dim n As Long
    Dim c As Byte
    Dim s As String

    n = ColumnNumber
    Do
        c = ((n - 1) Mod 26)
        s = Chr(c + 65) & s
        n = (n - c) \ 26
    Loop While n > 0
    ColumnLetter = s
End Function