For healthy chickens, I use about 30 drops to 1 gallon of water. If you have a sick chicken that you are dosing individually, I would do 1-2 drops in about 1/4 cup of water and squirt it down her throat, 3 times a day. I have also been known to just stick straight GSE in one of our silkie roosters mouths, as he sounded congested and I was afraid he was coming down with the coryza, but he is next to impossible to catch, so it was a one time deal. Next day he was fine and he never lost a beat.
That's what's working to keep my chickies healthy, you may find that you don't need quite that much or you may need more.
Also, on a side note, I discovered that they make GSE in pill form and it is awesome!!! That is what I am currently taking to get over a bad flu and it it working wonders without the bad taste.