It has to be in pounds. If you add up the numbers in various mixtures, they don't equal 100. Though some do, but the ratio is all that matters so it doesn't even matter if it's % or #. If you'll reply with a mix from that website, I can send you back the formula and results to get 300 #'s.
For good mixes start here. http://www.birdfarm.bravepages.com/starterx.html
And here's a good chart to see protein content off various ingredients. Instructions to find protein % at bottom of the website. http://www.avianaquamiser.com/posts/Protein_content_in_chicken_feed_ingredients/