The easiest method I've found for calculating how much a mold holds is to weigh the empty mold, fill it with water (like you did), and then weigh the full mold to find out the weight of water used. then when cutting your M&P soap blocks, cut enough to equal the weight of the full mold.
So if your empty mold weighs 10 oz and your full mold weighs 30 oz, then you need to cut off 20 oz of base to fill that mold.
__________________
Lyebrarian
