Brick size is an important standard in the construction and manufacturing industries.
The Core Concept: Coordinated vs. Work Size. Work Size (or Actual Size): The exact dimensions of the brick itself as it comes out of the kiln. Coordinated Size: The work size plus the intended thickness of the mortar joint (typically 10mm). Buildings are designed using coordinated dimensions so that everything fits to a neat grid, minimizing the need to cut bricks.
Here’s a detailed breakdown of brick sizes.

ISO Metric Coordinated Standard is the closest thing to a true international standard and is the basis for national standards in most of the world.
Basis: A 100mm (10cm) module for building dimensions.
Standard Coordinated Size: 200 mm (length) x 100 mm (width) x 100 mm (height)
Standard Work Size: 190 mm x 90 mm x 90 mm
The 10mm difference allows for a 10mm mortar joint. This means a course (row) of bricks will be exactly 100mm high, making planning incredibly efficient.

A: United States (ASTM Standards). The US uses the Imperial System and its standard is based on an 8-inch module. The most common brick is called "Modular".
Its work size is 7 ⁵⁄₈ x 3 ⁵⁄₈ x 2 ¹⁄₄ inches. When combined with a standard ³⁄₈-inch mortar joint, the dimensions become a neat 8 x 4 x 2⅔ inches. This allows the brick to fit perfectly with other building materials like concrete blocks, which are also based on an 8-inch module.
B: United Kingdom (BS EN 771-1). The UK standard is a great example of metricating a traditional imperial size.
The old imperial brick had a work size of 8½ x 4 x 2½ inches. This was directly converted to its metric equivalent: 215 x 102.5 x 65 mm. Adding a 10mm mortar joint gives the coordinated size of 225 x 112.5 x 75 mm.

Key Takeaway: Always confirm the local standard brick size with your supplier before starting a project. The "standard" brick in one country can be completely different from another.