Before we start, it is important to note that not every wrinkle needs to be removed. The thicker and less stretchy the fabric is, the less it will be possible to get rid of all of the wrinkles around the knees. Overfitting could actually limit your movements and prevent you from bending your legs!
If you have wrinkles all over the back of your legs, you might actually need to scoop out the back crotch curve (see “horizontal drag lines under the butt”). If your wrinkles are mostly around the knees, then you could be in one of the following situations.
Large wrinkles on the front and back of the pants above the knees, with more wrinkles at the ankles, mean that the legs are too long. Follow our tutorial on adjusting length to shorten them.
If the wrinkles on the front and back of the knees are small, and the pants are the right length with no wrinkling at the ankles, then the pants are too wide at the knees. Baste the sides of the legs, making sure to remove width equally on the inside and outside of each leg. Don’t forget to try on the pants to check that you can still bend the knees freely before you stitch these new seams.
Pattern-wise, this adjustment corresponds to grading down one or more sizes between the crotch point and the knee notches on the front (#1) and back (#2) pieces.
If you have a lot of wrinkles, but only on the back of the knees, then the back leg is too narrow on the upper calves. This might be the case if you have muscular calves. Here you need to add width to the back leg piece.
On the back leg piece (#2), grade up by one or more sizes, starting just above the knee. Don’t change anything to the front leg piece (#1).