Excel 2010, part of MS Office 2010 suite, uses Calibri 11pt font as default in a worksheet, header, footer, text box etc. However, if you are not a big fan of Calibri and/or like another font, you can easily change and use a different font face and size default in Excel.
To modify default font type/size in Excel
Open Excel, click File > Options. Under General category,under “When creating new workbooks”, you can set the desired letter face/type and font size to be used in Excel. When you finish, hit OK twice.
Existing worksheets retain previous font style preferences; you need to restart Excel for the change in font style to take effect.