20 fl. oz. Works best to spray in and around the coop too.
 
Mix 4 tablespoons per 1 gallon of water. Some use 3 Tablespoons and it works well.  (If using 4 TBS., the entire bottle will make 10 gallons) Shake well before each use.
You can also put a drop on the back of their neck, directly on the skin
Reapply in 2-3 weeks.