I don't know how much experience you have in casting but here's what I do. I have had success in keeping it simple, especially since I make most of my molds from cutting boards and they are random sizes and volumes. I use the first pour/use of the mold to figure out the amounts and weights for the future pours. I use clear plastic cups for casting so I can see through them and how much resin I'm pouring.
I start out by filling the mold with water to the level I want to use for casting, and dump that in a clear plastic cup. I place a mark on the cup and divide that amount in half (by ounces not weight, since resin weighs more than water. That will tell me roughly how much of part A and B resin is need in the cups to get the depth I want in the mold. I then pour the part A half in one cup and part B in another. Since B is heavier than A, I match their weights by pouring a little extra A and a little less B. After the first pour, you will know if you need to add or subtract a little by weight. Once you get the second pour down and the number fine tuned, write it on the side of your mold with a permanent marker or in a casting log for future pouring. Also, remember the amounts of resin will vary depending on what your casting. If your adding things like pinecones or acorn caps, they will require less resin than solid resin pours. Just make sure to dry the molds from the water before you pour the resin. Happy Casting!
