Foam concrete density chart
Dry density is the single number that fixes almost everything else about a foam concrete mix — strength, thermal conductivity and typical use. This chart runs the full working range in 100 kg/m3 steps, in both kg/m3 and lb/ft3, alongside the property ranges published elsewhere on this site.
Density reference table, 100 to 1600 kg/m3
Oven-dry density in 100 kg/m3 steps, with the 28-day compressive strength and thermal conductivity ranges for each, and a one-line indication of what that class is generally specified for. Strength and conductivity are property ranges, not single values, because void structure — not just density — sets where in the range an actual mix lands.
| Dry density | Dry density | 28-day fc | λ | What it can carry / typical use |
|---|---|---|---|---|
| 100 kg/m3 | 6.2 lb/ft3 | < 0.3 MPa | 0.04–0.06 W/(m·K) | Insulating fill, void and annulus filling, thermal breaks — no load |
| 200 kg/m3 | 12.5 lb/ft3 | 0.3–1.0 MPa | 0.06–0.09 W/(m·K) | Insulation boards, insulating roof screeds, sub-screed layers |
| 300 kg/m3 | 18.7 lb/ft3 | 0.3–1.0 MPa | 0.06–0.09 W/(m·K) | Insulation boards, insulating roof screeds, sub-screed layers |
| 400 kg/m3 | 25.0 lb/ft3 | 0.8–3 MPa | 0.09–0.18 W/(m·K) | Non-load-bearing blocks, floor screeds, trench reinstatement |
| 500 kg/m3 | 31.2 lb/ft3 | 0.8–3 MPa | 0.09–0.18 W/(m·K) | Non-load-bearing blocks, floor screeds, trench reinstatement |
| 600 kg/m3 | 37.5 lb/ft3 | 0.8–3 MPa | 0.09–0.18 W/(m·K) | Non-load-bearing blocks, floor screeds, trench reinstatement |
| 700 kg/m3 * | 43.7 lb/ft3 | ≈1.5–5 MPa | ≈0.13–0.25 W/(m·K) | Transition zone between classes — not separately published, verify by trial mix |
| 800 kg/m3 | 49.9 lb/ft3 | 2–8 MPa | 0.18–0.33 W/(m·K) | Load-bearing blocks in low-rise construction, wall panels |
| 900 kg/m3 | 56.2 lb/ft3 | 2–8 MPa | 0.18–0.33 W/(m·K) | Load-bearing blocks in low-rise construction, wall panels |
| 1000 kg/m3 | 62.4 lb/ft3 | 2–8 MPa | 0.18–0.33 W/(m·K) | Load-bearing blocks in low-rise construction, wall panels |
| 1100 kg/m3 * | 68.7 lb/ft3 | ≈4–12 MPa | ≈0.25–0.45 W/(m·K) | Transition zone between classes — not separately published, verify by trial mix |
| 1200 kg/m3 | 74.9 lb/ft3 | 5–25 MPa | 0.32–0.70 W/(m·K) | Precast elements, load-bearing panels, structural screeds |
| 1300 kg/m3 | 81.2 lb/ft3 | 5–25 MPa | 0.32–0.70 W/(m·K) | Precast elements, load-bearing panels, structural screeds |
| 1400 kg/m3 | 87.4 lb/ft3 | 5–25 MPa | 0.32–0.70 W/(m·K) | Precast elements, load-bearing panels, structural screeds |
| 1500 kg/m3 | 93.6 lb/ft3 | 5–25 MPa | 0.32–0.70 W/(m·K) | Precast elements, load-bearing panels, structural screeds |
| 1600 kg/m3 | 99.9 lb/ft3 | 5–25 MPa | 0.32–0.70 W/(m·K) | Precast elements, load-bearing panels, structural screeds — top of the foam concrete range |
The five density bands and their properties are set out in full, with drying shrinkage and water absorption behaviour included, on the density classes and properties page. This table exists to put every 100 kg/m3 step on one row for lookup and unit conversion; that page is the fuller reference.
Wet density versus dry density
Every density in the table above is oven-dry: measured after an element has lost its free water. Wet density — what a fresh batch actually weighs at the mixer — is always higher, because mixing water that has not yet left the material still counts toward the mass. The gap runs roughly 100 to 200 kg/m3 and widens sharply, in proportion, as target density falls: a 400 kg/m3 dry mix design predicts a wet density of 554 kg/m3 (a 38 % premium), while a 1000 kg/m3 mix predicts 1144 kg/m3 (a 14 % premium). The full derivation of both figures is on the mix design page.
Specify and accept material against dry density. Use wet density only as a same-shift production control — it is measured in minutes, dry density is not — and calculate its target separately for every mix design rather than borrowing a figure from a different one.
Converting kg/m3 and lb/ft3
The conversion factors used throughout this table:
1 kg/m3 = 0.062428 lb/ft3
1 lb/ft3 = 16.0185 kg/m3
Worked both ways from 400 kg/m3: 400 × 0.062428 = 24.97 lb/ft3, rounded to 25.0 lb/ft3 in the table above. Converting that rounded figure back: 25.0 × 16.0185 = 400.5 kg/m3, a fraction above the starting value purely because the intermediate figure was rounded to three significant figures. Carry an extra decimal place through intermediate steps if the round trip needs to close exactly.
Why strength follows density as a power law
Compressive strength does not fall in proportion to density; it falls faster. The relationship is a power law of the form f = a·ρn, with the exponent n typically between 2 and 3 for foam concrete. Halving the density therefore costs far more than half the strength:
| Exponent n | 0.5n | Strength remaining after halving density |
|---|---|---|
| 2.0 | 0.250 | 25 % |
| 2.5 | 0.177 | 17.7 % |
| 3.0 | 0.125 | 12.5 % |
In other words, halving density typically leaves somewhere between an eighth and a quarter of the original strength, not a half. The constant a and the exact exponent are specific to a given plant and mix, so this table shows only the shape of the relationship, not a number to design against. Where two mixes sit at the same density but different strengths, the difference is almost always void structure — finer, more uniform bubbles read as more strength at the same mass — which is a function of the foaming agent and how it is dosed, not of the binder content.
How to specify a density so it is enforceable
A density figure on its own is not a testable requirement. A specification that can actually be checked on site and at the lab states, at minimum:
- The target oven-dry density, with a tolerance — conventionally ±50 kg/m3 or ±5 %, whichever is greater.
- The minimum 28-day compressive strength that goes with that density, using the ranges above as a starting point and a trial mix to confirm the achievable figure for the chosen plant and foaming agent.
- The test method and moisture state at test, since a saturated specimen reads well below the same specimen at equilibrium.
- A wet density target and tolerance for production control, derived from the dry target using the mix design method, not copied from another mix.
Density alone tells a supplier what to weigh; the four points together tell them what to deliver, and give the buyer something to reject material against.
Where thermal performance is part of the specification, add the moisture state the thermal conductivity value applies to. A dry λ figure copied straight from this table into a U-value calculation for an in-service element will understate the real heat loss, sometimes considerably, because published values are almost always measured oven-dry and in-service material carries equilibrium moisture.
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