Changing Font Face and Size Conditionally

Robin asks if there is a way to use Excel's conditional formatting capabilities to change the font use in a cell or to change the font size in a cell. The short answer is no, that can't be done—at least not with conditional formatting. (The controls that allow you to specify font name and size are grayed-out in the formatting dialog box used with conditional formatting.)

You can, however, use a macro to examine cell contents and make changes in the appearance of a cell. Consider the following macro, which examines any cells you have selected when you run the macro. If any of the cells have a length of more than two characters or a value of more than 10, then the cell's font is changed.

Sub DoReformat()
    Dim rCell As Range

    For Each rCell In Selection.Cells
        If Len(rCell.Text) > 2 Or _
          Val(rCell.Value) > 10 Then
            rCell.Font.Name = "Arial"
            rCell.Font.Size = 16
        Else
            rCell.Font.Name = "Times New Roman"
            rCell.Font.Size = 12
        End If
    Next
End Sub

To use the macro, just select the cells you want changed and then run the macro. If you want the formatting to change more automatically, then you can have the macro check to see if a change was made within a certain range of cells:

Private Sub Worksheet_Calculate()
    Dim rng As Range
    Dim rCell As Range

    Set rng = Range("A1:A10")

    For Each rCell In rng
        If Len(rCell.Text) > 2 Or _
          Val(rCell.Value) > 10 Then
            rCell.Font.Name = "Arial"
            rCell.Font.Size = 16
        Else
            rCell.Font.Name = "Times New Roman"
            rCell.Font.Size = 12
        End If
    Next
End Sub

This macro, when added to the worksheet object, will run every time the worksheet is recalculated. It checks the range A1:A10, applying the same tests as in the previous macro. The result is that the formatting of the cells is checked and changed continuously. To have the macro check a different range, just change the addresses assigned to the rng variable near the beginning of the macro.

One drawback of this macro is that it can get sluggish if you have a very large range for it to check. It will go very quickly if you are checking A1:A10 (ten cells), but may go much slower if you are continually checking B2:N465 (over 6,000 cells). In that case, you may want to design the macro so it runs whenever the worksheet is changed, but only takes action if the change was done to a cell in your target range. The following version is also added to the worksheet object:

Private Sub Worksheet_Change(ByVal Target As Range)
    Dim rCell As Range

    If Union(Target, Range("A1:A10")).Address = _
      Range("A1:A10").Address Then
        Application.EnableEvents = False
        For Each rCell In Target
            If Len(rCell.Text) > 2 Or _
              Val(rCell.Value) > 10 Then
                rCell.Font.Name = "Arial"
                rCell.Font.Size = 16
            Else
                rCell.Font.Name = "Times New Roman"
                rCell.Font.Size = 12
            End If
        Next
        Application.EnableEvents = True
    End If
End Sub

The macro uses the Union function to check whether the cells changed (passed to the event handler in the Target variable) have any overlap with the range you want checked. If they do, then the checking is done on the cells in the Target range.

One thing to keep in mind with macros that affect formatting is that if you have conditional formatting applied to a cell that is also checked by a macro, the formatting in the conditional formatting takes precedence over the formatting in the macro. If your macro is changing font name and font size, this isn't a big concern because conditional formatting won't affect these attributes. However, if you change your macro to also change a different format attribute—such as cell color—and that attribute is also changed by the conditional format, then it won't look like the macro did anything because Excel uses the conditional formatting in preference to what the macro does.