Form factor refers to the linear dimensions and configuration of a device as distinguished from other measures of size, for instance, Gigabytes; a measure of storage size.

In computing, form factor is most often used to describe the size and format of PC motherboards, but also of hard drives, power supplies, cases, and add-in cards.

The term can also be used refer to the shape of a housing or package or mechanical connection associated with a device or mechanism within the context of its interface with other devices or mechanisms, also in regards to a human interface.