This would require an event macro. One way:

Put this in your worksheet code module:

Private Sub Worksheet_Calculate()
Range("A5").Font.Size = 8 - 2 * (Range("A1").Value 5)
End Sub

If you're not familiar with macros, see David McRitchie's "Getting
Started with Macros":

http://www.mvps.org/dmcritchie/excel/getstarted.htm

In article ,
"Steve Klenner" wrote:

Is there a way to change the font size in a cell based on results of a given
cell?

Ex....change font size from 10pt to 8pt in cell a5 if cell a1 is 5