For a solid cube with side length a and mass m:

The equations can be rearranged to solve for mass or side length when density is known.

Choose the variable to solve, enter mass and a side/diagonal measurement as appropriate, and select units. For a known material, use a density preset to estimate mass. For a measured sample, use actual mass and dimensions to determine density.

Mass is m=ρa³. Because side length is cubed, a small increase in dimension can cause a large increase in mass. Doubling side length increases volume and mass by a factor of eight when density stays constant.

If the side is not measured directly, geometry gives face diagonal=a√2 and space diagonal=a√3. The calculator can convert either diagonal back to side length before finding volume.

A measured metal cube can be used as a quick density experiment. Compare the calculated value with an appropriate material table, but remember that coatings, machining tolerances, alloy composition and internal voids can shift the result.

Concrete test cubes are useful for dimensional and mass measurements, but density varies with aggregate, entrained air, moisture and mix design. “Normal-weight concrete” is a range, not one magical universal number.

Density depends on the cube of the side measurement. That means dimensional error can be amplified in the computed volume. Use calipers or another suitable instrument when a small specimen requires precision, and measure multiple sides if the object is not perfectly cubic.

If length, width and height differ, the object is a rectangular prism rather than a cube. Use V=LWH and the general material-density or weight tool instead of forcing three unequal dimensions into a cube formula.

A metal cube has side 5 cm and mass 337.5 g. Volume is 125 cm³, so density is 2.70 g/cm³, consistent with aluminum-like material. If the same side dimension belonged to steel, expected mass would be much higher because density is about three times greater.

If side is entered in centimetres and mass in grams, density naturally comes out in g/cm³. If side is in metres and mass in kilograms, the result is kg/m³. The calculator normalizes units so you do not have to manually cube the length conversion factor.

Do not use diagonal length as though it were side length, do not forget that volume scales with side cubed, and do not assume a visually cubic sample has identical side measurements. Measure all relevant dimensions when precision matters.

Material presets are helpful for quick mass estimates. Aluminum is around 2700 kg/m³, many steels are around 7850 kg/m³, normal-weight concrete is roughly 2300–2400 kg/m³, and common plastics can range from under 1000 to well above 2000 kg/m³. These are reference values, not guaranteed values for every product.

Cube-density problems appear in classroom experiments, QA checks, concrete testing, metal identification, packaging estimates and manufacturing inspection. The same formula is simple, but the meaning of the measured volume changes if the cube contains pores, cavities or coatings.