How this instrument works
Mass equals density times volume: m = ρ·V, the multiplication that answers a question you can ask before the object you're weighing is even finished. Density is a property of the substance — a number pulled from a handbook or a material certificate, unaffected by how much or how little of the stuff there is. Volume is a property of the space that substance will occupy — a mold cavity, a tank, a poured footing — measured from a drawing, a dip reading, or a CAD model long before there is anything solid to set on a scale. Multiply the two and what comes out is the weight that object will eventually have, worked out in advance.
The relationship starts life the other way around: density is itself defined as mass divided by volume, ρ = m ⁄ V, a figure a lab produces by weighing a known volume once and writing the ratio down for later use. This instrument runs that definition in reverse, solving for the mass that a known density and a known volume must produce. Because the relationship is a straight multiplication, it stays perfectly linear at every scale: one litre of aluminium, at 2700 kg/m³, comes out to 2.7 kg, and two litres of the same metal weigh exactly twice as much — 5.4 kg — with no curve or correction anywhere along the line.
The formula trusts the density figure completely, so the honest limit sits there, not in the arithmetic. A foundry sizing a furnace charge from a mold's cavity volume should use the room-temperature solid density of the metal, because that's what the finished, cooled casting will actually weigh — the molten pour itself is less dense and shrinks further as it solidifies, which is why patternmakers cut cavities oversized rather than trusting this figure for pour volume. Bulk liquids drift the other way: a tank of diesel dipped on a hot afternoon holds a genuinely smaller mass than the same tank dipped cold, because the liquid has expanded into extra volume without gaining any weight — which is exactly why petroleum terminals correct a measured volume to a standard reference temperature before billing on it, rather than billing on the raw reading.
- Enter the material's Density in kg/m³ — switch to g/cm³ if that's how your handbook or certificate lists it.
- Enter the Volume — the mold cavity, the tank, the batch — in litres, millilitres, or cubic metres.
- Read Mass in kilograms, or switch to grams for a small sample or a lab quantity.
- For a metal pour, add your own allowance for gates, risers, and scrap loss; the figure here is net material mass only.
- For a stored liquid measured at an unusual temperature, correct the volume to the density's reference temperature first.
Worked example — sizing a one-litre aluminium casting
A patternmaker cuts a mold cavity that will hold exactly one litre of aluminium once the metal is poured and cooled solid — a small bracket casting, say. Aluminium's handbook density is 2700 kg/m³, and the instrument first turns the one litre into 0.001 m³. The formula does the rest: m = ρ·V = 2700 × 0.001 = 2.7 kg. That's the weight the finished, solid casting will read on a scale — worked out before the metal has even been melted.
That 2.7 kg is net metal in the finished part alone. A real furnace charge has to be larger, because the gating system — the sprue and runners that carry molten metal into the cavity, plus any riser that feeds shrinkage as the casting cools — also has to fill with metal and gets trimmed away afterward. Foundries account for this with a casting yield figure specific to their tooling, then melt enough stock to cover the net casting mass this instrument reports plus that overhead, rather than charging exactly 2.7 kg and coming up short at the mold.
Questions
How much extra metal should a foundry melt beyond the calculated mass?
More than this instrument reports, because the net casting mass it returns doesn't include the gating system. A common approach is to model the sprue, runners, and risers as their own volumes, multiply each by the same density, and add that to the casting's own mass — or apply a casting yield percentage built up from past pours of the same pattern. Either way, charging exactly the net figure into the furnace routinely leaves a mold half-filled.
Does this account for molten metal shrinking as it cools and solidifies?
No — the density this instrument uses is the room-temperature solid figure, appropriate for predicting what a finished, cooled casting will weigh, not for sizing the liquid pour volume. Molten metal is measurably less dense than the same metal solid, and shrinks further while solidifying, which is why pattern cavities are cut oversized by a shrinkage allowance rather than built to the exact dimensions of the finished part.
Why do fuel terminals correct a tank's volume for temperature before computing its mass?
Because mass is what's actually being bought and sold, and volume alone doesn't stay put as temperature changes. A litre of diesel measured on a hot day occupies more space than the same litre measured cold, without weighing any more, so custody-transfer measurement corrects the dipped volume to a standard reference temperature before multiplying by density. Skip that step and the same physical fuel appears to weigh a different amount depending on the weather.
What if my volume includes empty space, like the headspace above a liquid in a tank?
Leave it out — the formula only applies to material that's actually there. A storage tank's dip reading measures the liquid level, and its calibration tables convert that into the liquid volume below the surface alone; the vapor space above it has no meaningful mass to add, and including it in the Volume field only inflates the answer.
Can this be used for concrete, fuel, or other non-metal materials?
Yes — the formula doesn't care what the material is, only its density. Concrete at roughly 2400 kg/m³, times 3 cubic metres of it, comes out to 7200 kg before the rebar is even counted; the same instrument handles a fuel, a slurry, or a bag of grain equally well, as long as the density entered genuinely matches the material and its condition.
Why does the calculator ask for density instead of looking it up automatically?
Because one material name can cover a range of real densities, and only you know which one applies. '6061 aluminium' and aircraft-grade 7075 differ by a few percent; wet sand and dry sand differ by far more; a named steel alloy shifts with its exact composition and heat treatment. Entering the specific figure from your own material certificate or handbook keeps the mass this instrument reports trustworthy rather than approximate.