How this instrument works
Weight and size are connected by exactly one property that depends on what a piece is made of: density, the mass packed into each unit of volume. Two blocks cut to identical dimensions can weigh wildly different amounts if one is aluminum and the other is steel, because steel packs roughly three times as much mass into the same volume — density is the number that captures that difference and turns a size into a weight.
For a rectangular block — a cuboid — volume is simply length times width times height, the same formula from grade-school geometry. Multiplying that volume by the material's density gives weight directly: a bigger block or a denser material both push the answer up, and the relationship is a straightforward multiplication in every direction, with no rounding or approximation beyond whatever precision the density figure itself carries.
Getting the right density value matters more than getting the arithmetic right, since density varies meaningfully by material and even by alloy — mild steel runs around 0.284 lb/in³, aluminum around 0.098 lb/in³, and brass, titanium, various plastics and woods all sit at their own distinct figures. A shop or supplier quoting stock by weight, a rigger planning a lift, or an estimator pricing material by the pound all need the correct density for the specific material and alloy in hand, not a rough 'metal' or 'plastic' guess.
- Enter the block's dimensions into Length (in), Width (in) and Height (in) — any consistent orientation works, since multiplication doesn't care which dimension is called which.
- Enter the material's density into Material density (lb/in³) — look this up for the specific material and alloy, not a generic category.
- Read Weight for the resulting mass of the block in pounds.
- Double-check units before trusting the result — this instrument expects inches and pounds per cubic inch; feeding it feet or millimetres will give a wildly wrong weight without any warning.
Worked example — a 10×5×2-inch mild steel block
Enter 10 into Length (in), 5 into Width (in), 2 into Height (in), and leave Material density (lb/in³) at its default of 0.284 — the standard figure for mild steel. Weight reads 28.400 lb.
By hand: the block's volume is 10 × 5 × 2 = 100 in³, and multiplying by mild steel's density gives 100 × 0.284 = 28.4 lb exactly — the weight of a solid steel block that size before any drilling, cutting or hollowing reduces it further.
Questions
Where do I find the density figure for my specific material?
Machinery's Handbook and most metals or plastics reference tables publish density for common materials and alloys — mild steel is roughly 0.284 lb/in³, aluminum roughly 0.098 lb/in³, and brass, titanium, various woods and plastics each carry their own distinct figures. Use the value for the specific alloy or grade in hand rather than a generic category average, since density can vary meaningfully even within one material family.
Does this account for holes, pockets or other material removed from the block?
No — this formula computes the weight of a solid rectangular block with no material removed. If the actual part has holes drilled through it, pockets milled into it, or any other material taken away, the true finished weight will be lower than this figure; you'd need to subtract the volume of each removed feature separately before applying density.
What happens if I enter dimensions in feet or centimetres instead of inches?
The result will be wrong by whatever conversion factor separates your units from inches, since the formula performs no unit conversion on its own — it simply multiplies whatever numbers you enter. Convert length, width and height to inches, and make sure the density figure is in pounds per cubic inch (not per cubic foot or per cubic centimetre), before entering any values.
How much heavier is a steel block than the same-sized aluminum block?
Roughly three times heavier, since mild steel's density (about 0.284 lb/in³) is close to three times aluminum's (about 0.098 lb/in³) at the same volume. A 10×5×2-inch block that weighs 28.4 lb in steel weighs only about 9.8 lb in aluminum — the same size, cut from a lighter material, at roughly a third of the weight.
Can I use this for a shape that isn't a rectangular block?
Not directly — this formula assumes a simple rectangular cuboid, where volume is just length times width times height. A cylinder, sphere, or any other shape needs its own volume formula (πr²h for a cylinder, for instance) before multiplying by density; plugging non-rectangular dimensions into this formula will give an incorrect weight.