Yea, you definitely need a more accurate scale. I always do it by weight, and the cool thing about the metric system is that 1ml=1gr, so it's easy to figure out amounts. You can go to soapcalc.net to use for formulating an exact recipe. It's pretty simple to figure out.
Discussion
i have used that site before years ago. soap making is one of my minor obsessions. detergents and commercial soaps are garbage. it bugs me more than most people because i have sensitive skin and autoimmune problems.