In art, a mechanical line is a type of line that is created using a mechanical tool or device, such as a ruler or compass. Often, mechanical lines are created to be perfectly straight or curved, and they may also be of a consistent thickness or width. Because they are created with mechanical tools, and especially those created with a ruler, they may also be referred to as "straight lines."

As opposed to organic or freehand lines, which are usually expressive or fluid, mechanical lines are precise and uniform. They may be used to create a sense of order, structure, or geometry in an artwork. They can be also be used to depict technical or architectural forms.

Mechanical lines are common in technical drawings and architectural plans, where precision and accuracy are essential. They can also be used to create geometric patterns or motifs in decorative art. In contemporary art, mechanical lines may also be used in an ironic or subversive manner, to challenge conventional ideas of art and creativity.