October 17, 2022

How to do a full bum adjustment on the Meriam Trousers & Creston Jeans

Today, we’re helping those of you with bountiful bums get a great fit on the Meriam Trousers and Creston Jeans! Here’s how to do a full bum adjustment on the Meriam or Creston.

Meet the Meriam Trousers: woven pants you’ll actually enjoy wearing. The Meriam has the classic details you love in a trouser: a zip fly with a hidden closure, front slash pockets, straight legs, and optional back welt pockets. But best of all, you’ll get a fabulously comfortable fit with a flex waistband that gently expands as you sit down, plus the option of a full bum adjustment piece, already done for you.

Want even more fitting and sewing instruction? In our newest workshop, Pants Making for Curves, curvy fitting expert Jenny Rushmore takes you through the process of sewing a pair of Meriam Trousers, from choosing your size and fabric all the way to the final hem. With step-by-step video lessons and loads of fitting and sewing tips throughout, you’ll create your perfectly tailored trousers with confidence. This class comes with a free copy of the Meriam Trousers pattern.

How to do a full bum adjustment

The first good bit of news is that you may not have to do anything, as we’ve already included a separate “full bum” back piece which has a built-in 1″ full bum adjustment already done for you.

But what if you need more room in the back beyond that? No problem—you can do a full bum adjustment.

How much of an adjustment do you need to do?

The best way to calculate how much you need to add is to use half-body measurements and/or make a muslin.

1. Start by measuring your hip from “side seam to side seam” (where the side seams would be if you had pants on!) around the back and around the front of your body. If you need a full bum adjustment, you’ll likely find that the back measurement is bigger than the front measurement.


2. Take the front measurement, and multiply it by two, and use that number to make your starting muslin. For instance: if your front hip measurement is 24″ and your back hip measurement is 27″, you would take the front measurement and multiply it by two to get 48″, which is a size 18. Make up the muslin with a size 18 hip—we already know it will be too tight on the bum, but don’t worry!

3. To calculate how much we need to add horizontally around your body, subtract the hip measurement of the size you’re making (in this case, 48″) from your actual measurement (in this case, 51″) – so that would be 3″ in this example. Divide that by two – so in this case, 1.5″. That’s now “measurement A”. Alternatively, you can calculate this by making a muslin. Use a seam ripper to unpick the side seams from just below the waistband to your upper thigh. The seams will then spread apart. Make sure they’re evenly apart on either side of your pants, and then measure the width of the gap.

4. To calculate how much you to add vertically along the back, the easiest way is to make a muslin and measure: the back waistband is likely pulling down forming a “V” (because your bum also needs more length). To calculate how much you need to add vertically in your adjustment, measure how far down the back waistband is pulling from where it should be (level around your waist). This is now “measurement B”. Alternatively, you can measure your back rise (from the center of your crotch to the back where you want the trousers to sit) and compare it to the back crotch length on the pattern piece – the difference between these two numbers is “measurement B”.

So now we have a base starting size (18), the amount of horizontal addition that’s needed (measurement A) and the amount of vertical addition that’s needed (measurement B).

How to do a full bum adjustment

1. Mark the seam allowance around the edge of the back leg piece. Draw four lines:

    • Line 1 from the outer top corner of the waist, to the dart, and across to the crotch.
    • Line 2 through the center of the dart
    • Line 3 from the knee diagonally up to meet line 1 (the exact location is not crucial)
    • Line 4 vertically through the bottom of the crotch line and down.

2. Cut across Line 1, starting at the crotch, and going up to the top corner stopping at the seam allowance. Snip into the seam allowance from the other side to form a hinge. Cut down line 2, leaving a hinge at the end. Swing the upper pieces up so that the horizontal gap has parallel sides, and the gap is HALF of measurement B.

3. The upper part of the piece will now jut out past the lower part—adjust it so that it equals measurement A. If necessary, you can break the hinge on the dart apart if you need to spread the pieces further.

4. Cut down line 3 from the top, ending at the seam allowance and creating a hinge. Swing the piece over so that the two pieces of the crotch are lined up again.

5. Cut down line 4 from the top, ending at the seam allowance and creating a hinge. Swing it over, creating a gap HALF  of measurement B.

6. Trace the new pattern, re-drawing the dart using the original dart legs (the dart will now be wider). Re-draw the welt markings to be aligned again (don’t worry, you can always re-mark them once the dart is sewn when it’s a bit easier to see).

And that’s it! The waistline and side seams are exactly the same so there’s no need to adjust any other pieces.

Well done, you! Fabulous work doing a full bum adjustment on the Meriam Trousers. Now it’s time to cut your fabric and start sewing!

Want step-by-step video instruction with Jenny as your guide? Check out Pants Making for Curves, the latest online workshop from Cashmerette.

7 thoughts on “How to do a full bum adjustment on the Meriam Trousers & Creston Jeans

  1. Ljuba says:

    Hi there,
    I really appreciate you explaining this. I think I also have a low bum (aging) and so I find I tend to scoop the curve down as well. Do you have another method to deal with that? I have straight hips, but a curvy backside. My pelvis also tilts anteriorly (to the front).
    Also, can the top down centre out method work to solve some of these issues?
    Ljub a

    1. I haven’t done the TDCO method myself but it’s possible it could work! I think the main challenge is that it doesn’t introduce the tension created by having two legs, and if you have a prominent tummy or bum the fabric can tent out, not giving you an accurate read of the fit. For having a lower bum, I think scooping probably makes the most sense.

      1. Gigi says:

        “TDCO […] it doesn’t introduce the tension created by having two legs, and if you have a prominent tummy or bum the fabric can tent out, not giving you an accurate read of the fit.”

        So much this, Jenny!

        I’d add that the lack of tension at the crotch seam of a single leg pant also makes an accurate read of having a low butt, of full inner thighs and of legs positioned quite body centric difficult.

        TDCO gets me a perfectly fitting single leg pant within minutes, only to sew the two-leg pants and get the same dreaded folds as doing conventional changes and drape fitting.

    2. Gigi says:

      As someone with a low curvy butt and a tilted pelvis, I’d recommend shortening the back inseam and easing it to the front inseam. This was standard practice for patternmakers and tailors for decades but got somewhat either forgotten or not paid as much attention to in recent years, ofc with notable exceptions.

      1. Clare says:

        Gigi, what a brilliant tip! I assume that by “shortening the back inseam” you mean basically lowering the back crotch point?
        I have found that although scooping the back crotch curve (along with a substantial full-bum-adj) does somewhat improve the fit on my tilted pelvis and lower-with-age & very protruding butt, the fit is still not right.
        I’m now all fired up to make another Magna Pants toile using your tip before attempting the Meriam (no zipper or pockets to fuss with on the Magna.)
        I had no idea that this was standard patternmaking/tailoring practice once upon a time! Thank you!

  2. Lynn C Adesko says:

    My question is about the portion of line 1 from the bottom of the dart to the inside seam. Is that line supposed to be parallel to the top edge? Or perpendicular to the grain line? I’m looking forward to trying this.

    1. Perpendicular to the grainline!

Let me know what you think!