How this instrument works
Density is the one figure on this page you have to supply yourself. It opens at 1.00 g/mL — water's value, included as a familiar reference point — but resin, oil and filled mixtures rarely sit anywhere near that number, so the field exists specifically to be overwritten. A typical epoxy casting resin runs close to 1.1 g/mL, mineral oil sits near 0.85 g/mL, and a resin cut with lightweight filler can drop under 1.0 g/mL, all different enough from water that the default figure needs replacing before the pound result means anything.
Two-part casting resin systems — the kind used for river tables, jewelry molds and coaster art — specify their resin-to-hardener ratio by weight, not volume, because the chemical reaction between the two components depends on mass proportions, and even a small volume-based mismeasure can leave a batch under-cured or brittle. Resin and hardener are nonetheless sold and dispensed by the millilitre or fluid ounce, which means a caster who wants to verify a poured batch's weight, or who needs to state a finished piece's shipping weight, has to convert that volume through the blend's actual density.
Density isn't fixed even within one resin line: adding hollow glass microballoons to lighten a casting can pull the mixed density down toward 0.8 g/mL or lower, while mica powder or metal pigment stirred in for color pushes it upward instead. Manufacturers typically publish a mixed density figure on the product's technical data sheet, and that number — not the water default, and not a generic 'resin' average pulled from memory — is what belongs in this calculator's Density field for an accurate pounds result.
- Enter the volume into Volume (mL); 500 is preloaded as a typical resin batch size.
- Set Density (g/mL) to your product's mixed density from its technical data sheet — 1.00 is water, rarely the resin blend you're actually pouring.
- Read Mass (lb) for the resulting weight, recalculated instantly as either field changes.
- Estimating shipping weight? Add the container's empty weight to Mass (lb) for the total package weight a carrier will charge for.
Worked example — 500 mL at two densities
Enter 500 into Volume (mL) with Density (g/mL) left at its 1.00 default, and Mass (lb) reads 1.10231131093 — a 500 mL container of water weighs just over 1.1 pounds, a useful sanity check before converting an actual resin pour.
Change only Density to 0.8 g/mL, in the range of a resin batch lightened with glass-microballoon filler, and the same 500 mL now reads 0.88184904874 lb instead — roughly a fifth of a pound less for the identical volume, purely because the filled mixture is less dense than water. A caster relying on the water-based figure would overstate that batch's actual weight by exactly that margin on a shipping label.
Questions
Why is resin mixed by weight instead of by volume?
Because the cure reaction between resin and hardener depends on their mass ratio, not their volume ratio, and the two components rarely share the same density — mixing by volume alone can quietly throw off that ratio even when both cups look correctly filled. A digital scale and the manufacturer's stated weight ratio, commonly written as something like 2:1 or 3:1 resin to hardener by weight, produces a more reliably cured result than measuring by millilitre marks on a cup.
Where do I find my resin's actual density?
Its technical data sheet, usually published alongside the safety data sheet on the manufacturer's product page, states mixed density directly — often as a range, since batch-to-batch variation and ambient temperature both nudge it slightly. Where no data sheet is available, weighing a known volume of the already-mixed resin on a kitchen or lab scale and dividing grams by millilitres gives a workable figure for this calculator.
How much does adding glass microballoons or pigment change resin's density?
Enough to matter for a shipping-weight estimate. Hollow glass microballoons are added specifically to reduce a cast piece's weight, and a heavily filled mix can drop mixed density from roughly 1.1 g/mL toward 0.8 g/mL or lower, while dense mica powder or metallic pigment pushes the opposite direction. A calculator using an unadjusted water or generic-resin density will misjudge either kind of filled mix by a meaningful margin.
Can I use this to estimate a finished poured piece's shipping weight?
As a starting point, yes — convert the resin volume poured using its mixed density, then add the weight of whatever wood, pigment or embedded objects went into the piece along with the container or packaging it ships in. This calculator only accounts for the liquid resin's own weight, so a finished art piece's total shipping weight needs those other components added separately.
Is a lighter resin mix always the better choice for casting?
Not necessarily — lightweight fillers like glass microballoons reduce weight and can lower cost per pour, but they also change the cured piece's working properties, including strength, sandability and finish, compared with unfilled resin. The right density trade-off depends on the piece being made, not on weight alone, so filler choice is a design decision that happens to change the number entered here.
Why does the pound result matter more than millilitres for shipping a finished piece?
Because carriers charge by weight, or by whichever of weight and dimensional volume produces the higher billable figure, and a resin-heavy piece is often dense enough that actual weight, not size, sets the shipping cost. Knowing the resin's contribution in pounds ahead of a pour helps estimate that cost before the piece is even finished, rather than being surprised at the counter.