Density of Ceramics: Full Chart + What Density Predicts
Updated: Aug 22
Author: Mark Ma, Lead Materials Engineer at MAC Ceramic Technology. Expertise: Advanced Technical Ceramics, Precision Machining (±0.002 mm tolerances), and Industrial Materials Engineering. Reviewed for technical accuracy based on proprietary MAC Ceramic manufacturing data.
Quick Answer: The average density of technical ceramics ranges from 2.5 g/cm³ to 6.3 g/cm³, directly impacting the material's strength, thermal stability, and wear resistance. High-density ceramics like Zirconia (up to 6.1 g/cm³) are engineered for extreme durability, while low-density porous ceramics excel in thermal insulation.
Density of Ceramic Materials: Values, Measurement and What It Predicts
Ceramic Density Chart
Typical values for standard production grades, in g/cm³.
Material | Bulk density | Theoretical density | Typical relative density |
Advanced oxides | |||
Alumina 85% | 3.40 | 3.99 | 85% |
Alumina 96% | 3.72 | 3.99 | 93% |
Alumina 99.5% | 3.90 | 3.99 | 98% |
Alumina 99.9% | 3.95 | 3.99 | 99% |
Zirconia 3Y-TZP | 6.05 | 6.10 | 99% |
Zirconia Mg-PSZ | 5.70 | 5.80 | 98% |
ZTA (20% ZrO₂) | 4.10–4.30 | 4.35 | 96–99% |
Magnesia (MgO) | 3.50 | 3.58 | 98% |
Advanced non-oxides | |||
Silicon carbide (SSiC) | 3.10–3.15 | 3.21 | 97–98% |
Silicon carbide (RBSiC) | 3.05–3.10 | 3.21 | 95–97% |
Silicon nitride (GPSSN) | 3.20–3.25 | 3.21 | ~100% |
Silicon nitride (RBSN) | 2.40–2.60 | 3.21 | 75–81% |
Aluminium nitride | 3.26 | 3.26 | ~100% |
Boron carbide | 2.52 | 2.52 | ~100% |
Boron nitride (hot-pressed h-BN) | 1.90–2.10 | 2.28 | 83–92% |
Glass and traditional | |||
Fused silica | 2.20 | 2.20 | ~100% |
Macor (machinable glass-ceramic) | 2.52 | — | — |
Cordierite | 2.10–2.60 | 2.65 | 79–98% |
Steatite | 2.60–2.90 | 2.95 | 88–98% |
Porcelain | 2.30–2.50 | — | — |
Fireclay refractory brick | 1.80–2.20 | — | — |
For comparison: aluminium 2.70 · titanium 4.51 · steel 7.85 · stainless 8.00 · copper 8.96 · tungsten carbide 14.9–15.6 g/cm³.
Two things stand out. Most technical ceramics are lighter than steel — alumina at half the density, silicon carbide and silicon nitride at less than half. And relative density, in the right-hand column, is a better predictor of performance than the absolute figure, for reasons the rest of this page covers.
Three Densities, and Why the Distinction Matters
Ask a supplier for "the density" and you can get three different numbers. They are not interchangeable.
Theoretical density (also true or crystallographic density) is the density of the material with zero porosity, calculated from the unit cell: atomic mass divided by unit cell volume. Alumina's theoretical density is 3.987 g/cm³. It is a property of the compound and never changes.
Bulk density is the mass of a part divided by its total external volume, including all pores, open and closed. This is what you actually get, and it is what a datasheet should quote.
Apparent density is mass divided by volume excluding open pores but including closed ones. It sits between the other two and is used mainly for porous refractories.
Relative density — bulk ÷ theoretical, as a percentage — is the number that matters most:
Relative density (%) = (bulk density ÷ theoretical density) × 100
Porosity (%) = 100 − relative densityA 96% alumina at 3.72 g/cm³ has a relative density of 93%, so about 7% of its volume is empty space. A 99.5% alumina at 3.90 has 98% relative density and about 2% porosity. That difference in porosity is most of the difference in strength between the two grades — more than the purity difference itself.
Read datasheets carefully. "99.5% alumina" refers to chemical purity, not density. "98% dense" refers to relative density, not purity. They are different numbers describing different things, and they are frequently confused.
How Ceramic Density Is Measured
Archimedes method (ASTM C373 / ISO 18754) is the standard for fired ceramics and covers most of what you need:
Weigh the dry specimen (D)
Boil in water for 5 hours, or evacuate, to fill open pores
Weigh suspended in water (S)
Weigh saturated in air, surface wiped (M)
From these:
Bulk density = D ÷ (M − S)
Apparent porosity = (M − D) ÷ (M − S) × 100
Water absorption = (M − D) ÷ D × 100Geometric method — mass divided by measured volume. Fast, but only valid for simple shapes with good surface finish, and it ignores the distinction between open and closed porosity.
Helium pycnometry measures true density by gas displacement, penetrating pores that water cannot reach. Used for powders and highly porous materials.
Mercury intrusion porosimetry gives pore size distribution as well as total porosity. The most informative and the most specialised.
When comparing suppliers, confirm the method. A geometric density on a ground part and an Archimedes density on the same part will not agree.
General Density Range of Common Ceramics
Ceramic Type | Density (g/cm³) | Best Industrial Application | MAC Ceramic Solution |
Zirconia (ZrO₂) | 5.6–6.1 | High-wear components, pumps, valves | |
Alumina (Al₂O₃) | 3.6–3.9 | Substrates, electronics, wear parts | |
Silicon Nitride | 3.2–3.3 | EV components, high-temp engine parts | |
Silicon Carbide (SiC) | 3.1–3.2 | Extreme heat resistance, furnace components |
What Density Actually Predicts
This is where density stops being a specification and becomes useful.
Strength
Strength falls steeply and non-linearly with porosity:
σ ∝ (1 − P)ⁿ where P = porosity fraction, n ≈ 2–5At 5% porosity, a ceramic may retain 75–85% of its dense strength. At 10%, roughly 50–65%. At 20%, often less than a third.
The mechanism is straightforward: pores are pre-existing flaws. Ceramic strength is set by the largest critical flaw, and every pore is a candidate. A single 50 µm pore in a highly stressed region can govern the strength of the whole part.
Pore size matters as much as pore volume:
Pore class | Size | Effect on strength |
Micropores | <0.1 µm | Minor if isolated |
Mesopores | 0.1–1 µm | Contribute to failure initiation |
Macropores | >1 µm | Severe — act directly as critical flaws |
Two materials at identical 3% porosity behave very differently if one has that porosity as fine distributed micropores and the other as a handful of large voids.
Thermal conductivity
Pores scatter phonons, and gas conducts heat far worse than solid. Thermal conductivity therefore falls with porosity roughly as (1 − P)^1.5 to (1 − P)².
This cuts both ways. If you need a substrate to remove heat, specify maximum density. If you need insulation, porosity is the cheapest way to get it — which is why refractory insulating brick is deliberately made porous.
Elastic modulus
Falls with porosity, though less steeply than strength, and is essentially unaffected below about 20% porosity for many materials. Matters in precision fixturing and metrology, where stiffness rather than strength is the design driver.
Corrosion and permeability
Open porosity admits fluids into the bulk of the part, so corrosion attacks the whole volume rather than the surface. Closed porosity does not. Two parts at the same total porosity can have completely different service lives depending on whether the pores are connected.
For chemical service and for vacuum applications, apparent porosity and water absorption per ASTM C373 matter more than bulk density.
Weight and inertia
For moving parts, density is a direct design input. Silicon nitride bearing balls at 3.2 g/cm³ against steel at 7.85 have roughly 60% less mass, which cuts centrifugal loading at high speed and is a large part of why hybrid bearings run faster and cooler.
Why Density Varies Between Grades
Purity. Higher-purity powders sinter to higher density because they contain fewer refractory impurities that resist densification.
Sintering temperature and
time. Longer and hotter closes more porosity — but also grows grains, which reduces room-temperature strength. Every sintering schedule is a negotiation between these two.
Sintering aids. Small additions of Y₂O₃, MgO or CaO form a liquid phase at the grain boundaries during firing, dramatically accelerating densification. The cost is a residual glassy film that softens at high temperature and erodes in plasma.
Applied pressure. Hot pressing and hot isostatic pressing reach full density at lower temperatures and with a finer grain size. More expensive; often the only route to near-100% density in covalent materials.
Forming route. Reaction-bonded silicon nitride is the clearest example: RBSN sits at 2.4–2.6 g/cm³ (75–81% relative density) because reaction bonding produces no shrinkage, while gas-pressure-sintered Si₃N₄ reaches essentially full density. Same compound, very different materials.
Powder particle size distribution. A well-graded distribution packs more efficiently in the green body, giving higher green density and therefore higher fired density.
Full mechanism: structure of ceramic materials →
When You Should Specify Density on a Drawing
Not always — but in four cases, yes:
1. Structural parts near their strength limit. Specify minimum bulk density, because it is a proxy for the porosity that governs strength. It is also far easier and cheaper to verify on every lot than flexural strength.
2. Vacuum and pressure-containing parts. Specify maximum apparent porosity and maximum water absorption per ASTM C373. Open porosity means leakage.
3. Chemical service. Same reason — open porosity means corrosion through the bulk.
4. Rotating or reciprocating parts. Specify density directly as a mass and inertia input.
For general wear parts and insulators at modest stress, the material grade designation is usually sufficient.
Frequently Asked Questions
What is the density of ceramic materials? Technical ceramics range from about 1.9 g/cm³ for hexagonal boron nitride to 6.05 for zirconia, with most falling between 2.5 and 4.0. Traditional ceramics run 1.8–2.5. Tungsten carbide, at 14.9–15.6, is a cermet rather than a pure ceramic.
What is the density of alumina? 3.40 g/cm³ at 85% purity, 3.72 at 96%, 3.90 at 99.5%, and 3.95 at 99.9%. Theoretical density is 3.99, so the variation reflects residual porosity as much as composition.
What is the density of zirconia? 6.05 g/cm³ for 3Y-TZP and about 5.70 for magnesia-stabilised. Zirconia is the densest common technical ceramic — roughly 55% heavier than alumina — which matters for moving parts.
Are ceramics lighter than metals? Most technical ceramics are, considerably. Alumina at 3.9 g/cm³ is half the density of steel; silicon carbide and silicon nitride are closer to 40%. Zirconia at 6.05 is the exception among common grades, though still lighter than steel.
How does density affect ceramic strength? Strongly and non-linearly — strength scales roughly as (1 − P)ⁿ with n between 2 and 5. At 10% porosity, a ceramic may retain only half its dense strength, because pores act as pre-existing critical flaws.
How is ceramic density measured? By the Archimedes water-displacement method per ASTM C373 or ISO 18754, which gives bulk density, apparent porosity, and water absorption from four weighings. Geometric measurement, helium pycnometry, and mercury porosimetry are used for specific cases.
What is the difference between bulk and theoretical density? Theoretical density is calculated from the crystal structure and assumes zero porosity. Bulk density is what a real part measures, including its pores. Their ratio — relative density — is the most useful single indicator of ceramic quality.
Further Reading
Structure of ceramic materials — porosity and microstructure
Standards: ASTM C373 · ASTM C20 · ISO 18754
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