A film gauge refers to the width of the film stock. These measurements are what differentiates one type of film from another; 16mm and 8mm are among the common measurements of film gauges. While they both serve the same purpose, there are several distinct differences between them.
As their names state, 16mm film is double the width of 8mm film. As 8mm is smaller, it is able to have 80 frames per foot of film -- twice the 40 frames per foot of 16mm film. Despite this difference, both types of film have sprocket holes that are located in between each frame.
As 16mm film has a larger frame size, it allows more detail than 8mm film. It is also easier for 16mm film to achieve a shallow depth of field, which means that while a subject is sharp, the background remains soft, allowing the viewer to focus on the subject more easily.
Using 8mm film is more cost-effective as it is cheaper and able to capture more frames per foot than 16mm film. It is also cheaper to process than 16mm film.
Although 16mm film was originally for home use, after 8mm came onto the market, 16mm went on to be used for entertainment purposes, such as movies and travelogues. It was replaced by 8mm film for home use.