Density of Aluminum: Everything You Actually Need (g/cm³, kg/m³, lb/in³)

Pure aluminum has a density of 2.70 g/cm³, which is 2,700 kg/m³ at room temperature. In imperial units, that's 0.0975 lb/in³. Most aluminum alloys you'll actually work with fall between 2.64 and 2.81 g/cm³, depending on what's been added.

I picked up a 30cm square plate of 6061 once, maybe 6mm thick, tossed it slightly, and genuinely said out loud: "Wait, is this plastic?" It felt like a prop from a school play, not a real piece of metal. That moment is basically the entire reason aluminum is everywhere; it's that surprisingly light. Roughly a third of the density of steel. Not half. A third.

If you're here because something felt wrong, a part that should be heavy but wasn't, a weight calculation that doesn't add up, a spec sheet that gives you five different numbers in five different units, this guide sorts all of it out. You'll get the actual numbers, every alloy, the weight formula with a real worked example, and what causes these values to shift in practice.

Key Takeaways

• Pure aluminum: 2.70 g/cm³ (2,700 kg/m³ / 0.0975 lb/in³)
• Common alloys range from 2.64 to 2.85 g/cm³ based on alloying elements
• Aluminum is roughly one-third the density of carbon steel (7.85 g/cm³)
• 6061-T6, the most-used structural alloy, sits right at 2.70 g/cm³ — same as pure aluminum
• Temperature, casting porosity, and cold-working all shift these values slightly 

The Number, the Asterisk, and Why It's Not That Simple

Here's the honest version: 2.70 g/cm³ is correct, but it's the number for pure aluminum. Nobody builds structural parts from pure aluminum. It's soft. It bends too easily. You'd dent it opening a beer can.

Every piece of aluminum in an airplane, a bike frame, a food trailer, or a laptop enclosure is an alloy. Magnesium, silicon, copper, zinc — one or more of these get mixed in to harden it up. And those additions change the density. Not by a lot. But if you're calculating the weight of 500 parts for a manufacturing run, "not by a lot" can still throw you 10 kg off.

So here's what I'd tell a friend over lunch: use 2.70 as your starting estimate. Then look up the alloy number and refine it if precision actually matters.

Standard Reference Values at Room Temperature (~20°C)

Note: 1 g/cm³ = 1 g/mL. These are what the Aluminum Association uses as standard reference values.

Unit Conversion: Pure Al vs. Common Alloys

The one that trips people up is lb/in³. It's so small (0.0975) that it looks wrong. I double-checked it myself the first time.

Aluminum Alloy Density: By Series

The alloy designation system tells you what's been added to the aluminum. That first digit matters most for density. 2xxx means copper was added, which bumps density up. 5xxx means magnesium was added, which nudges it down slightly. 7xxx uses zinc, which is heavier, so density climbs.

Am I wrong, or does everyone assume 6061 is some special formula? It's not. The density of 6061 is literally the same as pure aluminum: 2.70 g/cm³. The magnesium and silicon additions happen to average out to the baseline. Convenient for calculations.

Density by Alloy Series

Why the 5xxx Series Is Lighter

Magnesium has an atomic density of 1.74 g/cm³ — lighter than aluminum itself. So when you mix it in, you actually pull the overall density below the baseline. That's why marine and automotive engineers reach for 5052 and 5083. Not just corrosion resistance. Actual weight savings on top of aluminum's already light starting point.

Why 7075 Is Heavier

Zinc sits at 7.13 g/cm³. Even in small percentages — about 5-6% in 7075 — it adds noticeable mass per unit volume. You get a denser alloy. But you also get tensile strength around 570 MPa, which overlaps with structural steel. That's the trade: pay a bit in density, gain a lot in strength. Rock climbers and aerospace engineers both decided it was worth it.

Aluminum vs. Steel, Copper, and Other Metals

This is why aluminum exists as a material category. Not because it's the strongest. Not the hardest. It just refuses to be heavy. And in a world where fuel costs money and people have to lift things, that matters more than almost anything else.

Steel is 7.85 g/cm³. Aluminum is 2.70. You're moving roughly a third the mass for the same volume. That's not a quirk. That's the whole business case for aircraft and performance vehicles.

Density Comparison: Aluminum vs. Structural Metals

One comparison worth sitting with: aluminum is only 2.7 times denser than water. Steel is nearly 8 times denser than water. That's why aluminum hulls and airframes make intuitive sense in a way that steel equivalents don't — you're working with a material that isn't fighting gravity quite as hard.

You're probably wondering about titanium. Titanium sits at 4.50 g/cm³ — heavier than aluminum, but with a strength-to-weight ratio that edges out both. The catch is cost. Titanium runs roughly 5–10 times more per kilogram and is significantly harder to machine. Aluminum hits the sweet spot: light enough, strong enough, affordable enough.

Why Aluminum Is Used for Power Lines (Not Just Structures)

In electrical work, aluminum's low density creates a specific advantage. It's twice as electrically conductive as copper per unit of mass. A copper power line of the same current capacity would be far heavier to suspend over long spans. That's why most high-voltage transmission infrastructure uses aluminum instead of copper — it's a density decision as much as anything else.

How to Calculate Aluminum Weight: Step by Step

Every weight calculation for aluminum parts comes back to the same equation. Once you have the density and the volume, you multiply. That's it.

The Formula:

Weight (kg) = Density (kg/m³) × Volume (m³)
Volume (m³) = Length × Width × Thickness

For imperial: Weight (lb) = Density (lb/in³) × Volume (in³)

Worked Example: Utility Trailer Floor Panel

Say you're designing a floor panel from 3mm aluminum sheet (6061). The panel is 2m long and 1.2m wide. Can one person move it?

Step 1: Calculate volume. V = 2.0m × 1.2m × 0.003m = 0.0072 m³

Step 2: Multiply by density. W = 0.0072 × 2,700 = 19.4 kg

One person. Manageable. Now run the same numbers for steel (7,850 kg/m³): W = 0.0072 × 7,850 = 56.5 kg

Two-person lift, minimum. For a panel you're installing solo, aluminum just made the job feasible.

Sheet Weight Comparison: Aluminum vs. Steel

Al 6061 at 2,700 kg/m³ vs. carbon steel at 7,850 kg/m³. Bold row matches the worked example above.

For odd shapes — pipe, extrusions, complex cross-sections — an online metal weight calculator built into most stock supplier catalogs handles all the geometry and unit conversion without making you convert between mm³ and cm³ mid-calculation.

What Actually Changes the Density Value

Last summer, I drilled precision holes in some 6061 bar stock. Everything fit perfectly. Then August came, the shop got hot, and suddenly the parts were binding in their fittings.

Wait — let me back up. What happened was thermal expansion. Aluminum expands more than steel when heated. About twice as much. The coefficient of thermal expansion for aluminum is 23.6 µm/m·°C. Steel is 11–12. So as the temperature climbs, aluminum grows faster, volume increases, and density drops — because density is mass divided by volume, and the mass doesn't change.

Temperature Effects on Aluminum Density

Approximate values for pure aluminum. Alloys vary slightly. Molten aluminum is about 12% less dense than solid at room temperature.

Manufacturing Process Effects

Cold-worked aluminum — rolled sheets, extruded rod, forged plate — has a compacted grain structure. It typically runs close to nominal theoretical density. Cast aluminum is different. Casting sometimes introduces tiny voids and porosity. That's why cast parts are quoted at 95–100% of theoretical density rather than exactly 100%.

If you're measuring a cast piece and getting 2.62 or 2.63 g/cm³ instead of the expected 2.70, that's not a measurement error. That's porosity. It's real, and it matters for structural calculations.

Anodized aluminum is another common question. Anodizing adds an aluminum oxide layer at the surface, thin enough (5–25 microns typically) that for any bulk or part weight calculation, you'd treat it as the same density as the base alloy. Negligible difference.

Other Factors That Shift Density

• Grain size: Finer grain structure from cold-working or heat treatment marginally increases packing efficiency
• Heat treatment (T6, T4, etc.): Precipitation hardening doesn't meaningfully change bulk density, though it moves atoms around within the lattice
• Impurities: Higher-purity 1xxx series alloys are slightly lighter than copper-bearing 2xxx grades for this reason
• Hydration: Rare in engineering contexts, but aluminum hydroxide compounds are less dense than metallic aluminum

The Full Alloy Reference Table

This is the table I wanted when I started doing engineering estimates and kept finding pages that listed only three or four alloys. Here's the real one — every major wrought grade you'll encounter, in the unit formats most useful for mechanical and structural work.

Density of Wrought Aluminum Alloys — Complete Reference

All values at room temperature (~20°C). Cast alloy A356 measured at 95–100% of nominal due to porosity. Bold rows are the most commonly specified alloys in general fabrication and machining.

There's a book I keep on my desk called Aluminum: Properties and Physical Metallurgy (edited by John Hatch, ASM International) that goes much deeper into why each alloy's elemental composition drives these density differences. If you're specifying materials for structural or aerospace work, it's worth having.

How to Measure Aluminum Density Yourself

You can do this in any shop with basic tools. The method depends on the shape of your part.

For Regular Shapes (Plate, Rod, Bar, Sheet)

Measure dimensions precisely with a caliper. Calculate volume. Weigh on a scale. Divide mass by volume.

Example: a square bar 50mm × 50mm × 200mm. V = 0.050 × 0.050 × 0.200 = 0.000500 m³ If it weighs 1.35 kg → ρ = 1.35 ÷ 0.000500 = 2,700 kg/m³

You just confirmed 6061.

For Irregular Shapes: Water Displacement Method

Submerge the part in a container of water. Measure how much the water level rises. That displaced volume equals your part's volume. Then weigh, divide. Done.

Here's the thing I got wrong the first time: aluminum is soft. I was gripping a small cast fitting to hold it underwater, and put a small dent in it. That changes the volume. Very slightly, but still. Use a fine mesh basket or tie a string around the part so you're not gripping machined surfaces directly underwater.

Interpreting Your Result

If you're getting 2.62–2.63 on a cast part when you expected 2.70, that's porosity from casting. Not a bad measurement.

Why Density Matters Beyond Just Weight

I almost skipped this section. But honestly, it's more interesting than the numbers table, so here we go.

Low density doesn't just mean light. It means aluminum is easy to recycle. Denser metals need more energy to melt and separate from impurities. Aluminum melts at 660°C and takes significantly less energy per kilogram to process in a recycling stream. The material keeps all its mechanical properties after recycling, too. That's not a coincidence — it's the density doing economic and environmental work at the same time.

There's also an acoustic angle. Aluminum speaker diaphragms are used in high-end audio drivers because sound travels through aluminum at about 6,420 m/s — much faster than through steel or polymer. A lighter, stiffer diaphragm that moves cleanly produces a cleaner high-frequency response. The low density is doing acoustic work, not just structural work.

And the strength-to-weight story — 7075-T6 aluminum hits around 570 MPa tensile strength at 2.81 g/cm³. Structural steel hits 400–550 MPa at 7.85 g/cm³. Aluminum delivers comparable strength per unit of volume at less than 36% of the weight. That's why commercial airframes aren't built from steel, even though steel is stronger in raw tensile terms. You'd never get airborne.

Specific Strength Comparison (Tensile Strength ÷ Density)

This is the table that explains why aerospace and performance vehicles exist the way they do. 7075 aluminum is nearly four times more efficient than carbon steel at carrying load per kilogram of structural weight.

The Nerd Section: Atomic Weight vs. Volumetric Density

Ever notice how density and atomic weight sometimes tell different stories? Aluminum has an atomic weight of 26.98 g/mol — fairly light on the periodic table. Iron's atomic weight is 55.85, more than double that of aluminum. But iron's face-centered cubic crystal packing is tight enough that the per-atom volume difference compounds into the density ratio you see (2.70 vs. 7.85).

Aluminum's crystal structure is also face-centered cubic. That's a reasonably efficient packing arrangement. The combination of lightweight atoms and decent packing efficiency lands you at 2.70 g/cm³.

Here's the counterintuitive part: silicon has an atomic mass of 28.09 — slightly heavier than aluminum's 26.98. But silicon atoms in an aluminum-silicon alloy occupy more volume per atom, which keeps the bulk density from rising. That's partly why the 4xxx series (silicon additions) ends up lighter than some other alloy families despite silicon being slightly heavier at the atomic scale. Packing geometry matters as much as atomic mass does.

The alloy additions you really need to watch are copper (63.55 g/mol) and zinc (65.38 g/mol). Both are substantially heavier atoms. When they replace aluminum atoms in the lattice — even at 5–6% — they pull the bulk density up noticeably. That's the 7075 and 2024 story in atomic terms.

Frequently Asked Questions

What is the real density of aluminum? 

Pure aluminum is 2.70 g/cm³ (2,700 kg/m³). "Real" in the sense of what you'd measure on a high-purity annealed sample in a lab. Alloys range from 2.64 to 2.85 g/cm³ depending on composition.

What is the density of 6061 aluminum in kg/m³? 

2,700 kg/m³. Same as pure aluminum. The magnesium and silicon additions in 6061 happen to average out to the same baseline density, which makes it easy to use as a reference point.

What is aluminum density in lb/in³? 

0.0975 lb/in³ for pure aluminum and 6061. For 7075, it's 0.1015 lb/in³. These are the values you'll see on ASTM spec sheets and machining reference books.

What is the true density of aluminum in g/mL? 

2.70 g/mL. Since 1 cm³ = 1 mL, the values are identical. This comes up in chemistry and lab contexts more than engineering ones.

Is aluminum alloy 100% aluminum? 

No. By definition, an alloy is a mixture. 6061 is roughly 97.9% aluminum with the remainder being magnesium, silicon, copper, chromium, and other trace elements. Only the 1xxx series (like 1100) approaches 99%+ purity, and even those have controlled impurity limits.

What is the volume of 1 kg of aluminum? 

Using 2,700 kg/m³: Volume = 1 ÷ 2,700 = 0.000370 m³ = 370 cm³. That's slightly less than a standard 375 mL beverage can. 1 kg of steel, by comparison, would only occupy about 127 cm³.

What is 7850 kg/m³ density? 

That's carbon steel. 7,850 kg/m³ is the standard engineering reference for mild and structural steel. It's almost exactly 2.9 times denser than aluminum at 2,700 kg/m³.

What are the top 3 densest metals? 

Osmium (~22.59 g/cm³), iridium (~22.56 g/cm³), and platinum (~21.45 g/cm³). For practical engineering contexts, tungsten (~19.3 g/cm³) is the densest widely used structural metal. All are roughly 7–8 times denser than aluminum.

How to measure the density of aluminum? 

Weigh the piece, find its volume (by geometric measurement or water displacement), and divide mass by volume. A clean 6061 piece should return 2.70 g/cm³ ± 0.02.

What is the density of aluminum in kg/cm³? 

0.00270 kg/cm³. Same value as g/cm³ numerically, just with different units — since 1 g/cm³ = 0.001 kg/cm³, and 2.70 × 0.001 = 0.00270 kg/cm³.

All density values are at room temperature (~20°C) unless otherwise noted. Reference: Aluminum Association alloy standards and ASM International materials data.