Coasters, bookmatched blanks, spheres, pyramids, and multi-cavity trays. Pick the shape, enter the size and how many cavities, and get the total mixed resin split into part A and part B.
For an irregular or organic mold, fill it with water, pour into a measuring cup, and enter that volume directly — see the note below.
Each shape uses its own volume formula: a box is length × width × depth, a cylinder is π × radius² × height, a full sphere is (4/3) × π × radius³, a hemisphere is half of that, a cone is (1/3) × π × radius² × height, and a pyramid is (1/3) × base length × base width × height. The calculator multiplies one cavity by your cavity count, then adds the waste margin. One US gallon of mixed epoxy fills 231 cubic inches and one fluid ounce fills 1.805 cubic inches.
For organic shapes — waves, geodes, figurines, anything that is not a clean geometric form — the formulas only approximate. Instead, fill the empty mold with water, tip it into a measuring cup, and read the volume. That measured volume is exactly the resin the cavity holds. Dry the mold thoroughly before pouring resin, since trapped water ruins the cure.
If you are embedding an object, the resin fills only the space around it. Measure the full cavity volume, then subtract the object's volume. The quickest way to find that object volume is displacement: note the water level before and after dropping it into a filled measuring cup.
Resin left behind on the cup and stir stick is unavoidable, and topping off a cavity is easy while running short is not — a mid-pour refill can leave a visible layer line. Five to ten percent extra is usually enough; fresh, unsealed silicone can grab a bit more on the first pour.