The easiest method is the water displacement method: fill your mold with water, then pour that water into a measuring cup. The water volume equals your mold's internal volume. For complex shapes, you can also fill the mold with dry rice or sand, then measure that in a graduated cylinder. Our calculator handles the math once you have the dimensions or direct volume measurement.

The mixing ratio indicates how many parts of Part A (resin) to combine with Part B (hardener/catalyst). A 1:1 ratio means equal amounts of both components. A 2:1 ratio means two parts resin to one part hardener. Always follow the manufacturer's specified ratio—incorrect proportions can result in sticky, soft, or brittle castings that never fully cure.

A waste factor (typically 5–10%) accounts for resin that clings to mixing cups, stir sticks, and silicone pouring spouts, as well as minor spills and bubbles. Without this buffer, you risk running short mid-pour—which can ruin a casting. For intricate molds with many undercuts or when using fast-curing resin, consider a 10–15% waste factor.

Yes! Multiply the volume (in ml) by the resin's density (g/cm³). Most epoxy resins have a density of approximately 1.1–1.2 g/cm³, meaning 100 ml weighs roughly 110–120 grams. Polyurethane resins typically range from 1.0–1.1 g/cm³. Always check the manufacturer's Technical Data Sheet (TDS) for the exact density of your specific resin.

1:1 resins are generally more forgiving—they're easier to measure by volume and cure reliably even with slight mixing errors. They're great for beginners, shallow casts, and coating applications. 2:1 resins often produce harder, more durable castings with better heat resistance and clarity, but they require more precise measuring. Deep-pour epoxy resins frequently use 2:1 or even 3:1 ratios to control exothermic heat generation during curing.

Our calculator provides exact volumes for regular geometric shapes (prisms, cylinders, spheres, cones). For irregular or organic shapes like figurines, geodes, or jewelry bezels, we recommend using the Direct Volume mode—measure your mold's capacity using water displacement, then enter that known volume directly. This bypasses geometric approximation entirely and gives you the most accurate resin estimate.

For precision casting, metric units (milliliters and grams) are recommended—they're more granular and reduce rounding errors. US crafters often use fluid ounces. Our calculator supports inches, centimeters, and millimeters for dimensions, and displays results in ml, fl oz, and cubic inches simultaneously so you can work in whichever system you prefer.