How is the size of a screwdriver typically defined?

The size of a screwdriver is typically defined by the length of the blade. This length determines how deep the screwdriver can reach into various fasteners and helps ensure that it can effectively engage with the screw head. The specific blade length can also affect torque and leverage when turning a screw. While other factors, such as the width of the tip and the diameter of the handle, contribute to the overall usability and comfort while using the screwdriver, the blade length is the primary measurement that defines its size and appropriate application for different fastening tasks.