Flexural Modulus Formula

The formula for finding a flexural modulus eludes me. However, the folks at http://www.tpub.com/content/engineering/14071/css/14071_301.htm have just what you are looking for. They list the procedure in conducting a flexural-strength test. You will also find out how to calculate the modulus of rupture. While you are there, be sure to check out the links they provide as well. I am sure you will .