The word “pants” is a generic term that refers to three principle categories, of fit between the waist and crotch, jeans, slacks, and trousers—all pants—look and fit differently. Each is designed with varying amounts of ease to specifically accommodate different activities or purposes.
Let me try and define the difference between the three. Jeans, slacks, and trousers. Once you understand the difference, you will know which one is best for you.
The distinguishing difference between jeans, slacks, and trousers is the length of the crotch extension, which affects the way the pants fit or conform to the body.
Traditional jeans have the shortest crotch extension because they closely contour the body in front and back. Body shape and figure variances are very visible. Jeans are designed for activities with a lot of movement and where a tight fit is needed. Usually described as close fitting, jeans are a fitting challenge. Jeans are not your best choice if you are going to be sitting all day.
Slacks have a crotch extension that is longer than jeans but less than trousers. Slacks slightly contour the tummy and buttocks. Body shape is somewhat visible, and the slacks cup under the buttocks. Many pattern companies use this type of pants for their basic fitting shell because it allows you the flexibility to contour the fit closer to jeans or looser like trousers. Slacks are usually described as fitted or semi-fitted.
Trousers have the longest crotch extension, conform the least to the contours of the body, and are the easiest pants to fit. They hang straight from the hip. Alterations are usually unnecessary if weight fluctuates slightly. Trousers are usually described as loose to very loose fitting.
Selecting the correct type of pants pattern will go a long way toward giving you the silhouette you want, as well as needed comfort. As a rule, the more the pants conform to the body, the harder they are to fit. Because of the basic design differences between the three types of pants, I do not recommend that you take trousers pattern and try and fit it like jeans, or vice versa. For ease of fitting and sewing, consider choosing a pattern with limited pleats or gathers at the waist and a straight or wide leg. Whether you are a beginner or an experienced sewer, this silhouette is complementary to a majority of figure types and is adaptable to all skill levels, depending on the details you select.