Mixing own feed,, protein calculating

[FarmalI]

I need help.. I mix my own feed but I would like to know what the protein is. Can anyone help me find a program or formula that I can use to fine the protein of 3 or more ingredients?
Thanks

 

[Clay Mudd]

I use a variation of this spreadsheet:

http://www.backyardpoultrymag.com/2-3/harvey_ussery1/

It's pretty easy to plug in values and tweak the recipe as needed.