Plaster Calculator

This tool helps you estimate how much plaster and water you need for a casting mold. Plaster is traditionally mixed by weight: about 100 parts plaster to 70 parts water. One quart of water (≈2 lb) plus 2.85 lb of plaster yields roughly 80 cubic inches of mixed plaster. Enter the dimensions of your mold below; the calculator will estimate the weight of water and plaster required. You can also add extra (10–20%) to account for spills.