I've been experimenting, but I think it's about 8oz water to about a tablespoon of Dr. B's. I can tell when I didn't add enough - it feels like I'm washing my hands with water, and the foam just disappears quickly. When I do add enough, the lather spreads well, and my hands feel very moistened. I'm so glad I made the switch - I haven't needed to moisturize my hands since then, and my excema has gotten so much better!