Things You'll Need
Instructions
Determine the shape or combination of shapes that most closely resemble the desired mold. If you are casting a model house, the main part of the house would be a cube and the roof would be a pyramid.
Use the measuring tape to determine the dimensions of the shapes.
Calculate the volume of each shape in cubic inches. For the house example, you would determine the volume of the main part of the structure by multiplying its length by the width by the height. The volume of the roof would be determined by the formula: Volume of the pyramid = 1/3 x base length x base width x height.
Add the volumes of the individual shapes that combine to make the desired mold.
Find the density of the casting material in cubic inches. The density of iron, a common casting material, is 0.26 pound per cubic inch. The density of iron is 0.29 pound per cubic inch, while concrete is 2.3 pounds per cubic inch.
Multiply the total volume of the mold by the density of 1 cubic inch of the casting material.