A trowel and bricks.
Brick sizes are standardized sizes used by brick manufacturers to ensure products remain consistent and reliable. Masons working with bricks can theoretically determine the amount of coverage needed along with the desired look and then order a certain number of bricks in a set size for the job. However, brick sizing is immensely complicated, and despite the fact that it should be standardized, it actually isn’t.
The first thing to be aware of when discussing brick sizes is that there are different standards for facing bricks and paving bricks. Paving brick is the brick used for walkways and patios, while exposed brick is used for making walls. Sometimes the same term will be used to talk about two different sizes of paving and facing brick. For example, many nations have a so-called “standard” size, which is quite different depending on whether you are talking about exposed brick or paving brick.
The next thing to be aware of is that brick sizes vary considerably from country to country. The size of a “standard” front brick, for example, is far from standard, which can become a serious problem when people are ordering bricks from different countries. A standard Italian brick and an American standard brick, for example, are not the same size, which means that a course that mixes such bricks will not be uniform.
As if that were not enough, the names of the sizes of the bricks are also not standardized, even in the same country. The “jumbo” brick of one company can be the “economy” of another company, for example. This means that the supposed standards that apply to brick sizes are effectively meaningless, because one cannot use standard terms and assume that someone will know what size is being discussed.
Finally, the bricks are scaled in nominal and actual size. The actual size refers, as you can imagine, to the actual measured size of the brick, and it is given in three dimensions, length, width and height, so that people understand the size and shape of the brick. The nominal size, also given in length, height and width, is the size calculated with the gaskets, but as gasket sizes vary, the nominal sizes are also not uniform in nature. For this reason, companies often list both sizes of bricks so people know exactly what they are buying.
As brick sizes are not standardized, it is preferable to ask brick manufacturers to simply provide the dimensions of their products when placing an order. Most companies also indicate the area a given number of bricks can cover by estimating the average joint size between the bricks, and people can also use a brick calculator to determine how many bricks they need to order for a project. As always, asking for surpluses in case the bricks break or the measurements are slightly off is a very good idea.