Every garment has its own individual sizing specifications. These sizing charts can be viewed in the online catalogue under each product. Please click on the appropriate online catalogue to view the specific size.  
Despite all these measurements, the good old tried and true method is to grab your favourite fitting shirt, lay it down on a flat surface and measure from arm to arm across the chest and compare the measurement to the size here.  Usually 2.5cm below the arm hole is where you measure the chest across. The length measure point is from high shoulder point to bottom of hem. This can be viewed by clicking on the relevant links below.