Density turns a geometry into a mass and underpins buoyancy, stress, and cost estimates. This reference lists typical densities for metals, plastics, woods, ceramics, and liquids in both common unit systems, and converts a volume into a part mass.
How it works
Density is mass per unit volume. The table gives each material in grams per cubic centimetre and the identical figure in kilograms per cubic metre — the two differ by exactly 1000:
kg/m^3 = g/cm^3 * 1000To estimate a part’s mass the tool multiplies the chosen density by the volume you enter:
mass (g) = density (g/cm^3) * volume (cm^3)So a 50 cm³ aluminium bracket at 2.70 g/cm³ has a mass of 50 * 2.70 = 135 g.
Why density is critical across engineering disciplines
Density connects geometry to several fundamental engineering quantities:
- Structural analysis: Dead load = volume × density × gravity. A concrete floor slab at 2,300 kg/m³ generates predictable self-weight that must be carried by beams and columns.
- Buoyancy: An object floats if its average density is less than the fluid it displaces. Steel (about 7,900 kg/m³) is denser than water (1,000 kg/m³), but a steel ship floats because its total volume (including interior air) makes its average density less than water.
- Material cost estimation: Material cost = mass × cost per kilogram. Choosing aluminium (2.70 g/cm³) over steel (7.85 g/cm³) for the same part saves about 66% of material mass — important for both cost and weight-sensitive design.
- CNC and 3D printing: Feed-rate and print-time estimates depend on how much material is being moved or deposited, which is a density-driven calculation.
- FEA (finite element analysis): Almost every FEA solver requires density as an input property alongside elastic modulus and Poisson’s ratio.
Typical densities: quick reference
Some values that come up most frequently in design work:
| Material | Density (g/cm³) | Notes |
|---|---|---|
| Water (4°C) | 1.000 | Reference standard |
| Aluminium 6061 | ~2.70 | Most common structural alloy |
| Mild steel / carbon steel | ~7.85 | Varies slightly with carbon content |
| Stainless steel 304 | ~7.93 | |
| Copper | ~8.96 | |
| Titanium (grade 5 / Ti-6Al-4V) | ~4.43 | High strength-to-weight ratio |
| PLA (3D printing) | ~1.24 | Common FDM filament |
| ABS | ~1.05 | |
| HDPE | ~0.95 | Lighter than water — floats |
| Oak (dry) | ~0.60–0.90 | Species and moisture dependent |
| Pine (dry) | ~0.45–0.60 | |
| Concrete | ~2,300 kg/m³ | Varies with mix and aggregate |
Why densities vary for the same material
The values in this reference are representative midpoints, not exact constants. Real materials vary for several reasons:
- Alloy composition: Adding copper to aluminium (to make 7075) raises its density slightly; adding silicon (for 4000-series) also changes it.
- Temper and heat treatment: Heat treatment changes microstructure but has minimal effect on density.
- Moisture content in wood: Green (freshly cut) wood is much denser than kiln-dried lumber. Values in this table are typically for air-dry wood.
- Porosity: Cast metals often have internal porosity that lowers effective density compared to wrought material.
- Fluid temperature: Water is densest at 4°C (1.000 g/cm³) and less dense at both higher and lower temperatures.
Common unit conversion traps
Keep units consistent when computing mass. The most common mistake:
- Density in kg/m³, volume in cm³: the result is not kg. Convert volume to m³ first (1 cm³ = 1×10⁻⁶ m³), or convert density to g/cm³.
- Density in g/cm³, volume in mm³: divide by 1,000 to get grams (1 cm³ = 1,000 mm³).
The safest approach: work in one unit system throughout. g/cm³ pairs naturally with cm³ → grams; kg/m³ pairs with m³ → kilograms.