Mold Making Calculator (Sculpture) Calculator

Making a mold means covering the sculpture's entire outer surface, so the real driver of material cost here is surface area, not volume — this calculator estimates that surface area using the Knud Thomsen approximation for an ellipsoid's surface (a well-known closed-form formula that's more accurate than cruder methods for organic, rounded forms), derived from your sculpture's half-height, half-width, and half-depth. A detail multiplier then inflates that raw surface figure for more complex pieces — up to 50% extra for highly detailed work with many undercuts — since fine texture and re-entrant surfaces require more silicone to fully capture. Silicone volume is that effective surface area times a wall thickness that steps up with sculpture size (3/8 inch for pieces under 18 inches tall, up to 5/8 inch for anything over 4 feet), then converted to gallons and pounds using silicone's typical density of about 10.8 lb per gallon, and priced per pound according to whether you chose tin-cure, platinum-cure, or urethane rubber — platinum-cure runs roughly 55% more per pound than tin-cure ($28 vs. $18/lb) but resists cure inhibition better.

A separate mother mold — the rigid outer shell (plaster bandage or fiberglass) that holds the flexible silicone's shape during casting — is sized off the same surface area at a fixed quarter-inch shell thickness. The suggested number of mold pieces (2, 4, or 6) and the labor-hour estimate both scale with your chosen complexity level, since more undercuts mean more parting lines and more time. Treat all of this as a materials-and-time planning estimate: real molds for asymmetric or deeply undercut forms may need custom piece-mold strategies this formula can't fully anticipate.