The stroke volume is a part of the working space of the cylinder in a reciprocating internal combustion engine, which is defined by the piston's bottom and top dead centers. Simply put, the stroke volume is the volume the piston fills during its stroke.

However, as many people mistakenly think, the stroke volume does not mean the engine's total displacement. It only indicates the volume of the cylinder's working space defined by the piston's bottom and top dead centers. Above the top dead center of the piston, there is a space called compression space or compression volume…

The compression ratio is one of the basic characteristics of a piston combustion engine, which indicates the cylinder volume ratio between the piston in the bottom and the piston in the top dead center.

The compression ratio is thus the ratio of the entire working volume of the cylinder to the volume of the compression space. In other words, the ratio between the volume of the mixture sucked into the cylinder and the volume of the mixture compressed in the cylinder.