Adding Centre Back-Leg Seams To Trouser Patterns

Lately, I’ve been adding centre back-leg seams to trouser patterns, usually on a slim or skinny-leg design, and I discovered that it helped me improve the fit for my rather flat, low bottom. I got a couple of requests in the comments for a dedicated post about how I did this, so here we are. Happy to oblige 🙂

As I said, I tend to use this extra seam (often called a Princess seam) for slim or fitted leg designs. I’ve pretty much mastered the fit of wide-leg styles of trousers, and I have a couple of go-to patterns that I use a lot, but the fitted styles have always been the ones to cause me more problems. As well as a flat, low bottom that tucks under, I tend to stand with my knees pushed back and my calves pushed out. Add that to my slight knock knees, and it’s a recipe for some weird fabric pulls and creases back there.

Creating a seam down the back of the legs enables you to do some subtle shaping under your bottom and at the knees and calves. I probably wouldn’t use this kind of seam on a wider trouser or a straight-leg formal style, but on a casual skinny pant in a fabric with a little stretch, it’s ideal. Here’s how I do it:

Adding Centre Back Leg Seams To Trouser Patterns

1 First, you need to locate the centre of the back leg pant pattern. Usually, the grainline is drawn here, but if it isn’t, locate the centre of the hem and draw a vertical line up to the waistline.

2 I’ve been using elasticated waist patterns, but if there is a dart at the waist, you need to incorporate it into the new seam. See the green lines indicating the new dart in the above image. Depending on the shape of your pattern piece, you may feel as though the new seam line gets too close to the middle of the back waist. If this happens, I would probably leave the original dart placement where it is.

3 Next, you’ll need to draw new grainlines for each side of the back trouser pattern. You’ll also need to create some notch markings along your new seamline to enable good seam alignment when sewing it back together. See the blue grainlines and green notches:

4 Now you can cut through your pattern and add seam allowances to your two new pattern pieces.

5 Now you can make a test garment and do your adjustments at the new back leg seam. A very common one is to take a little underneath your bottom, removing some of that fullness that can sometimes happen back there.

I also like to create some shaping over my calves at the back. I take in the seam a little behind my knee and then add a little extra at the full part of my calf, and then I bring the seam in at my ankles. Something about the way that I stand with my calves pushed back can throw off the way my trousers sit, and it makes funny diagonal wrinkles from front knee to back calf, so by altering things at the back, it gets rid of those pesky wrinkles.

Here are the pattern pieces for the divided back pattern of my SA Sage trousers:

Note how the pieces slope out at the bottom in the middle and how I compensated for that amount by taking a bit off each side at the bottom. They look wonky in flat pattern form, don’t they? But here’s the side view of them being worn, showing no weird diagonal wrinkles when on my body:

And here’s a back view of my other Sage trousers showing the back seams and only minimal crinkling under my bottom to allow for normal movement.

So that’s it, thanks for reading, and I hope you found this post useful. Or maybe it’s something you’ll consider using for a future make. Don’t forget to bookmark it for reference 🙂

I’ll see you soon!