MS Excel 2007 by default uses the Body Font font in font size 11. When you type data in a worksheet, text box, header or footer, it will appear as the Calibri font in font size 11). If you want to change the default font and font size for all new workbooks that you create, do the following -
-Go to Excel options (Microsoft Office button-> Excel options)
-Under popular category, under When Creating New Workbooks, in the use this font box, click the font that you want to use.
In the font size box, enter the font size that you want to use.
You will not be able to use the new font and font size until you restart excel. The new default font will be operational only after you restart excel. The existing workbooks will not be affected. However, if you want to use the new default font, you can move worksheets from an existing workbook to a new workbook.