Aggregate concrete masonry units, which include concrete blocks, are governed by British Standard BS EN 771-3, according to the Concrete Block Association (CBA). In terms of requirements for specifying dimensions, they must be stated in terms of length, width and height, in that order.
Concrete blocks are manufactured from different concrete mixes and contain varying amounts of air, according to the University of the West of England, Bristol. Air makes the blocks lighter and affects their mechanical properties, including strength. The air content is a designed feature, governed by the concrete mix and processes used. Manufacturers can thereby offer customers blocks of standard size for a wide range of different structural applications.
The usual size for aerated, medium density, dense and foundation concrete blocks is 440 x 215 x 100 mm (17 x 8 x 4 inches). Usefully, this is approximately the same length as two house bricks and the same height as three house bricks. Where building plans require a mix of block work and brick work, the need for cutting is reduced, saving time and money.
A concrete block with a face size of 390 x 190 mm (15 x 7 inches) is also standard, according to the CBA. Smaller blocks have become popular partly because of health and safety regulations governing working practices. Tarmac, amongst other manufacturers, provide concrete blocks of differing widths. The face side, or the side on show, is 440 x 215 mm (17 x 8 inches), which is standard. The various block widths available are 75, 90, 100, 140, 150, 190 and 215 mm (3, 3.5, 4, 5.5, 6, 7.5 and 8.5 inches).
Concrete bricks are, essentially, smaller versions of concrete blocks. However, some have frogs, which are the shaped indentations in the top and/or bottom to grip the mortar. The standard size for concrete common bricks is approximately 215 x 103 x 65 mm (8.5 x 4 x 2.5 inches). There are some slight variations to the “standard” size of concrete bricks, just as there are for clay bricks.