Metal density.

Mass in a fixed volume.

Density is how much mass fits in a given volume. It is the reason a sheet of steel and a sheet of aluminum the same size feel so different in the hand.

For a quick comparison, aluminum alloys are around 2.7 g/cm³, carbon steel around 7.85 g/cm³, and 300-series stainless around 8.0 g/cm³. Use the metal density chart for individual grades and values in lb/in³, or jump to the part-weight calculation. These are typical comparison values; use the specified grade and actual dimensions for your part.

Two things set it: how heavy the atoms are and how tightly they pack. Iron atoms are about twice as heavy as aluminum atoms and pack a little closer, so steel comes out at roughly 2.9 times the density of aluminum. Polymers are long chains of light carbon, hydrogen, oxygen and nitrogen atoms with space between them, so they sit near 1 g/cm³ — about the density of water.

Because it depends on the atoms, density hardly changes with processing. Cold rolling, annealing, quenching and tempering move a steel from 250 to 1,400 MPa of yield strength while its density stays within about 1%. Alloying changes it slightly: lithium makes some aerospace aluminum lighter; zinc and copper make 7075 a little heavier than 6061.

You will also see specific gravity: density relative to water. It has no units, and for practical purposes equals density in g/cm³.

Metal density chart: aluminum, steel and stainless steel.

On a density chart, families collapse into narrow bands. That is the most useful single fact about density: to change a part's weight substantially, you change family, not grade.

Titanium sits between aluminum and steel at about 4.5 g/cm³; copper alloys are the heaviest common metals at 8.5–8.9. PTFE is the dense outlier among plastics at about 2.2, because its fluorine atoms are heavy.

How it is measured.

The usual method is Archimedes' principle: weigh a sample in air, weigh it again submerged in water, and the difference gives its volume. ASTM B311 covers this for powder-metal and other metals; ASTM D792 for plastics. For a simple machined block, measuring the dimensions and weighing it works too.

For 3D-printed and cast parts the measured density can be below the material's theoretical value because of porosity. HP quotes MJF PA-12 parts at about 1.01 g/cm³ — essentially solid nylon 12 — so a print that weighs noticeably less than its volume predicts is a sign of incomplete fusion or internal voids.

How engineers use it.

Weight estimates

The everyday use is simple: volume × density. A 24″ × 12″ × 0.125″ blank of 5052 is 36 in³, which at 0.0968 lb/in³ is about 3.5 lb. In steel it would be about 10.2 lb. Weight drives shipping cost, handling, the size of the hardware holding it and — for anything that moves — the energy and force needed to move it. The calculator below does the arithmetic; our material weight calculator handles full sheets and stock shapes.

Lightweighting: never density alone

Swapping steel for aluminum does not make a part 65% lighter unless strength and stiffness do not matter. Aluminum has a third of steel's stiffness, so a panel that has to stay as stiff needs to be thicker. The right comparison is a performance index — a property divided by density:

This is why aircraft skins, vehicle panels and enclosure lids go to aluminum: for a flat panel loaded in bending, the thicker aluminum part is still about half the weight of the steel one. See specific strength and Young's modulus for the details.

What it means in fabrication.

• Price per part. Metal is bought by weight, so density converts a price per pound into a price per part. Stainless and copper are expensive per pound and heavy.
• Handling. A 4 × 10 ft sheet of 0.25″ steel weighs about 408 lb; the same sheet in aluminum about 141 lb. Weight decides whether a sheet goes on the laser by hand or by loader.
• Laser cutting. Density is one of the factors in how much energy it takes to melt a given kerf, but reflectivity and thermal conductivity matter more — aluminum is lighter yet harder to cut than steel at the same thickness.
• Shipping. Freight is priced by weight and size; for large flat parts, switching to aluminum can cut freight as much as material.

Common mistakes.

• Assuming the same gauge number means the same thickness. Gauge tables differ between steel, galvanized and aluminum; weight-per-area tables tied to gauge are material-specific. Work in decimal thickness — see the gauge chart.
• Using bulk density for printed or cast parts. Porosity and infill lower the real figure.
• Lightweighting by density alone. A lighter material that has to be twice as thick may save nothing — compare the performance index for the load case.