AAC Block Density: Classes, Chart and Test

AAC block dry density is usually between 300 and 800 kg/m³, against 1,200–1,800 kg/m³ for brick masonry in the Bangladesh HBRI AAC masonry manual. China’s GB/T 11968-2020 sorts blocks into grades B03 to B07 (mean dry density up to 350–750 kg/m³), India’s IS 2185 (Part 3) uses bands from 451 to 1,000 kg/m³, and EN 771-4 leaves the manufacturer to declare a value.

Density is the property everything else follows: strength, thermal conductivity, weight on the structure, and how much raw material each cubic meter consumes. This guide puts the density classes of the main standards in one chart, explains the difference between dry density and the weight of a delivered block, and shows how density is tested.

AAC Block Density Chart (GB/T 11968-2020)

GB/T 11968-2020 is the standard most Chinese-built lines are designed to. The 2020 edition dropped the B08 grade, so five density grades remain. Each grade is limited by its mean dry density, can carry only certain strength classes, and has a maximum thermal conductivity in the dry state.

These values are as cited in the T/CASME 2022 draft group standard, which is built on GB/T 11968-2020 (the 2023 Hunan draft standard uses partly different thermal conductivity limits for its own high-precision blocks); check the current edition of GB/T 11968 before writing them into a contract. The strength classes and their test method are covered in AAC block compressive strength.

AAC Block Density in Other Standards

IS 2185 (Part 3), India

IS 2185 (Part 3):1984 (reaffirmed) groups blocks by oven-dry density and sets strength and thermal conductivity for each band.

The thermal conductivity limits are higher than in GB/T 11968 at the same density. Part of the difference is that IS 2185 measures in the air-dry condition, where pore moisture raises conductivity, while GB/T 11968 states dry values. Do not compare the two columns directly.

EN 771-4, Europe and the GCC

EN 771-4 has no density classes. The manufacturer declares the gross dry density in kg/m³, and may also declare minimum and maximum individual values and, where relevant, the net dry density. The CEN catalogue summary of EN 771-4:2011+A1:2015 notes that tested dry density may not differ from the declared value by more than ±50 kg/m³ (check the current edition). Density is tested to EN 772-13. The GCC adopted EN 771-4:2011 as GSO EN 771-4:2021. As one published example, H+H UK declares a gross density of 730 kg/m³ and λ10,dry of 0.16 W/(m·K) for its High Strength Celcon block. For more on declarations, see our EN 771-4 guide.

DMS 1 Part 3, Dubai

Dubai Municipality’s DMS 1: Part 3: 2014 also has no density classes. The manufacturer declares the maximum gross density of each block type, which must not exceed 850 kg/m³, and test results to BS EN 772-13 must not exceed the declared value.

ASTM C1693, United States

ASTM C1693 pairs each strength class (AAC-2 to AAC-6) with nominal dry bulk densities and density limits. Check the current edition (C1693-11, reapproved 2025) for the figures.

Dry Density vs the Weight of a Delivered Block

Every standard above specifies density in the dry or oven-dry state. A block on a truck is not dry. It leaves the autoclave wet and dries slowly, so its real weight on delivery is higher than the dry density suggests.

An illustrative calculation for a 600 × 200 × 200 mm block (0.024 m³) of grade B05:

The same logic applies to a pallet. On our reference line a mold is split into two stacks of about 1.5 m³ each, so by the same estimate (1.5 m³ × 550 kg/m³) a B05 stack weighs about 825 kg dry and over 1,000 kg at 30% moisture. That matters for forklift and truck loading, for dead load on slabs during construction, and for how a buyer checks density: a delivered block must be dried before its weight says anything about its grade.

Density, Strength and Thermal Conductivity: The Trade-Off

Lower density means more pores. More pores mean lower thermal conductivity and lower weight, but also lower strength. In GB/T 11968-2020, B03 can only carry A1.5, while A5.0 needs at least B05. The plant’s choice is not “the lighter the better” but which grade meets the market’s strength requirement at the lowest density your raw materials allow.

• Infill walls in hot climates: thermal performance often drives the choice. Dubai’s DMS 1 Part 3 asks manufacturers of blocks used in thermally rated elements to declare thermal conductivity at 35 °C and 60% relative humidity, a condition closer to Gulf service than the dry 10 °C value used in Europe.
• Markets with a strength minimum: Dubai requires 3.2 N/mm² average normalized compressive strength. If your raw materials only reach that at B06, B06 is your product, whatever the brochure says about lightness.
• Load-bearing markets: higher density, higher strength, and usually a declared value under EN 771-4.

AAC Block Density Test: Step by Step

The details differ by standard, but a dry density test follows the same sequence. This is the GB/T 11969-2020 method, with the equivalents noted.

1. Sample blocks at random from the lot, as the product standard requires (for example, six blocks per lot of 20,000 under DMS 1 Part 3).
2. Cut specimens. GB/T 11969-2020 cuts 100 mm cubes from the center of the block along the rise direction at three heights: the top cube 30 mm below the top face, one at the center, and the bottom cube 30 mm above the bottom face. Density varies over the height of the cake, so one cube is not enough.
3. Measure each specimen’s dimensions and calculate its volume. GB/T 11969-2020 allows ±1 mm on specimen dimensions.
4. Dry to constant mass in a ventilated oven, following the drying steps in the method (check the current edition for the temperatures). Weigh the dry specimen.
5. Calculate dry density = dry mass / volume, in kg/m³, and average the specimens.
6. Compare the mean with the grade limit (GB/T 11968), the band (IS 2185), or the declared value (EN 771-4, DMS 1 Part 3).

EN 771-4 and DMS 1 Part 3 use EN 772-13, which tests whole units or specimens for gross and net dry density. IS 2185 (Part 3) uses IS 6441 (Part 1). If you also want moisture content, weigh the specimens before drying: moisture by mass = (wet mass − dry mass) / dry mass.

How Thermal Conductivity Is Tested

When you compare λ values from two suppliers, check the method and the moisture condition first. A dry value and an air-dry value for the same block are not the same number.

What Controls Density in the Plant

Density is set by the recipe, not by the machinery. The mass of dry solids poured into each mold, the aluminum dosage (about 0.45 kg per m³ of finished product on our reference design), the water-to-solids ratio and the slurry temperature decide how far the cake rises and how fine the pores are. A line can make several density grades from the same equipment by changing the recipe; on our reference line the range is B03–B07.

What the equipment must deliver is consistency: accurate weighing, stable slurry temperature (45–48 °C at pouring on our reference design), and a pre-curing room that holds 40–50 °C. Uneven rise gives density differences between the top and bottom of the cake, which the three-height sampling in GB/T 11969 will find. If you plan to sell to more than one standard, plan your AAC block sizes and density grades together, because both are fixed in the cutting and recipe settings.

FAQ

What is the density of AAC blocks in kg/m³?

Most AAC blocks have a dry density between 300 and 800 kg/m³. GB/T 11968-2020 grades them B03 to B07, with mean dry density limits of 350 to 750 kg/m³. IS 2185 (Part 3) covers 451 to 1,000 kg/m³ in five bands. EN 771-4 and Dubai’s DMS 1 Part 3 use a declared value; DMS caps it at 850 kg/m³.

Is AAC block density the same as its weight per m³ on delivery?

No. Standards quote dry density, measured after oven drying. Delivered blocks still hold water from autoclaving, so they weigh more. A B05 block at 550 kg/m³ dry weighs about 30% more at 30% moisture by mass. To check the grade, dry a sample to constant mass first.

What does B05 or B06 mean for AAC blocks?

They are GB/T 11968 dry density grades. B05 means a mean dry density of no more than 550 kg/m³, and B06 no more than 650 kg/m³. Each grade can carry only certain strength classes: B05 can be A2.5, A3.5 or A5.0, and B06 can be A3.5 or A5.0.

Which AAC density is best for walls?

It depends on what the wall must do. Lower density gives better insulation and lower weight; higher density gives more strength. For infill walls, the lowest grade that meets your market’s strength minimum is usually the right choice. For load-bearing walls, the structural engineer sets the strength, and the density follows.

How is AAC block density tested?

Specimens are cut from sampled blocks (GB/T 11969 uses 100 mm cubes from three heights in the block), measured, dried to constant mass, and weighed. Dry density is dry mass divided by volume. EN 771-4 and Dubai’s DMS use EN 772-13; IS 2185 uses IS 6441 (Part 1).

Planning an AAC Block Plant?

Which density grades you can sell depends on your raw materials and your market’s standard. See our AAC block production line for the process and product range, and the AAC block plant setup guide for the full planning sequence.

Sources

• GB/T 11968-2020, Autoclaved aerated concrete blocks (China) — SAMR national standards catalog entry
• GB/T 11969-2020, Test methods of autoclaved aerated concrete — preview (Chinese Standard)
• GB/T 11968-2006 / 2020 revision notes — preview (Chinese Standard)
• T/CASME draft (2022), Lightweight compressive and durable aerated block — National Group Standards Platform
• DBJ 43/T (draft, 2023), Technical standard for application of high-precision AAC blocks — Hunan Province
• IS 2185 (Part 3):1984 — Bureau of Indian Standards
• IS 2185 (Part 3):1984, text — Internet Archive
• EN 771-4:2011+A1:2015, Autoclaved aerated concrete masonry units — CEN catalogue entry (iTeh)
• GSO EN 771-4:2021 — GCC Standardization Organization
• DMS 1: Part 3: 2014, Autoclaved aerated concrete masonry units — Dubai Municipality
• ASTM C1693-11(2025), Standard Specification for Autoclaved Aerated Concrete — BSI Knowledge
• H+H UK, High Strength Celcon Block declaration of performance
• Eco Friendly AAC Block Masonry Manual — Housing and Building Research Institute, Bangladesh