You have checked your measurements against Safran’s size chart, and ended up with a difference of one, two, or even three sizes between your hips and waist? Do not worry, here is how to grade from one size to another when tracing the pattern!
Start by taking all your measurements carefully: natural waist, high hips (the widest point of your stomach) and low hips (the widest point of your butt). Write down these values, along with the corresponding sizes, for instance:
Trace the waistband pieces (3 and 4) in the size corresponding to your waist measurement. Trace all the single-size pieces as well (5, 6, 7, 8, 9, 11). Trace the back pocket (10) in the size corresponding to your hips (the largest of the high-hips and low-hips sizes).
Trace the top of the back piece in the size corresponding to your waist measurement (here, size 38). On the right-hand side of the pattern piece, draw a line connecting the top corner to your high-hips size (here, size 40), joining at the first notch. Still on the right-hand side, connect the first notch to the second notch in your low-hips size (here, size 42).
On the left-hand side, at the tip of the crotch curve, mark the size corresponding to your low-hips measurement. Draw a new crotch curve joining this mark to the top of the piece, which was traced in your waist size (here, 38).
Use your low-hips size to trace the rest of the back leg. You will be able to adjust the lower leg directly later on, by basting along each seam (make sure to leave enough ease to be able to bend your knees!). If you have very thin legs compared to your hips, you can choose to go down a size or two below the knee directly on the pattern.
Trace the top of the front piece in the size corresponding to your waist measurement (here, size 38). Shift the pocket opening to the left so that the lower edge of the pocket opening meets the line corresponding to your high-hips size of the left-hand side of the piece (see figure above).
Trace the left-hand side of the front pants in your hips size. Trace the fly in your waist size, then draw a new crotch curve connecting it to the tip of the crotch in your hips size (see figure above on the left). Trace the rest of the leg in your hips size.
Like with the pants back, trace the left-hand side of the pattern piece in your high-hips size down to the first notch, then draw a curve joining your low-hips size at the second notch. On the right-hand side, shift the lower part of the fly sideways towards your high-hips size (here, size 40; don’t forget to move the mark indicating the end of the zipper as well!). Trace the tip of the crotch in your low-hips size and draw a new crotch curve to connect it to the fly (see figure above on the right). Trace the rest of the leg in your low-hips size.
The only step left is to modify the pocket (8) and pocket top (9). When we traced the pants front, we shifted the pocket opening towards the size corresponding to the high-hips measurement. We now need to adjust the top of the pocket to end up with the correct waist measurement. For instance:
Don’t forget to do the same adjustment to the pocket top!