EngineerBenchFinding density, mass, or volume
Density is mass divided by volume. If two of those quantities are known, the third follows directly: multiply density by volume for mass, or divide mass by density for volume. Select the unknown first and keep the unit labels attached to your measurements.
Use the volume occupied by the material
For a hollow part, the outside bounding volume includes empty space. Use net material volume when estimating solid-material mass. For powders or porous material, a bulk density includes the voids and should not be confused with the density of the solid substance.
Choosing a density value
A representative material density is suitable for an initial estimate, but it is not a certificate for a particular grade or batch. For purchasing or shipping, include coatings, inserts, and other parts separately if they are not included in the entered mass or volume.
Checking the units in a density calculation
A density of 1 g/cm³ is equivalent to 1,000 kg/m³. The factor is large because both the mass unit and the cubed length unit change. Convert the complete density unit rather than converting only the numerator. A one-liter volume at 1,000 kg/m³ has a mass of one kilogram, which is a useful arithmetic check when comparing unit selections.
If density is being measured, subtract the container's mass and use a volume method appropriate to the sample. A bounding box around an irregular object normally overstates solid volume. Trapped air, pores, or absorbed liquid can also change what a displacement measurement represents. For a mass estimate, multiply each distinct material volume by its own density and add the masses rather than averaging unrelated densities without weighting. Small errors in volume can strongly affect a measured density, particularly for small samples. Keep the original measurement precision in mind when deciding how many digits of the calculated value to report.
Formula
Density = mass / volume.