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.

Interactive density explorer

Move the slider to any dry density and the readouts and chart below update to show its strength band, thermal conductivity band, typical use and two derived comparisons. Every figure comes from the reference table below — this is a different view of the same data, not a separate source.

Reading the chart

The unit toggle above relabels these axes in pcf, psi and BTU·in/(h·ft²·°F) without changing the chart's geometry — the bands are the same physical data on the same logarithmic scale; only the tick values and axis titles switch to match the selected system. In US practice, 150 lb/ft³ (150 pcf) is the conventional normal-weight reference, equivalent to 2400 kg/m³, and is the baseline the weight-saving figure uses once US units are selected.

Both axes are logarithmic because both properties span more than two orders of magnitude over the working range: compressive strength runs from well under 1 MPa at 100 kg/m³ to 25 MPa at 1600 kg/m³, and thermal conductivity runs from around 0.04 to 0.70 W/(m·K) over the same span. Plotted on a linear axis, the low-density end would flatten into a single line against the pixel grid and the differences that matter most in that range — between, say, 100 and 300 kg/m³ — would be unreadable. On a logarithmic axis, equal ratios occupy equal distances, so a doubling of strength looks the same size whether it happens at the bottom or the top of the range.

The shaded band at each density is not measurement noise. Two mixes at the same dry density can differ in strength by a factor of several, and that spread is the band width: it comes from void structure and binder content, the variables a foaming agent and a mix design actually control, not from scatter in a test method. A narrow trial-mix result sitting confidently inside the band is a real, specific mix; the band itself only bounds what is achievable at that density across normal practice.

The dashed rectangles are reference materials, not foam concrete, included for scale. Autoclaved aerated concrete overlaps foam concrete on density but sits higher on strength for a given density and lower on drying shrinkage, because it is cured differently. Lightweight aggregate concrete starts roughly where foam concrete's working range stops and extends the density-strength relationship upward using a porous aggregate rather than entrained air. Normal-weight concrete sits at the top of the chart, around 2400 kg/m³, as the reference point the weight-saving figure above is measured against.

One honest caveat applies to every conductivity figure on this page and in the chart: the values are dry. Thermal conductivity rises with moisture content in service, sometimes considerably, because water conducts heat far better than the air trapped in the pore structure. A dry λ figure read straight off this chart into a U-value calculation for an in-service wall or roof will understate real heat loss; treat it as the baseline, not the design figure, and apply the appropriate moisture correction for the application.

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.

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:

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:

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:

1. The target oven-dry density, with a tolerance — conventionally ±50 kg/m³ or ±5 %, whichever is greater.
2. 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.
3. The test method and moisture state at test, since a saturated specimen reads well below the same specimen at equilibrium.
4. 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.

Last reviewed: 7 September 2026