Tutorial: Easy ways to create a roomier trouser crotch

March 20, 2015 by ThreadTheory 16 Comments

Let’s say you have just sewn up a muslin of the Jedediah Pants or Jutland Pants pattern (or any other trouser pattern) and notice strain lines radiating from the fly of the trouser when you try the muslin on.  The trousers seem to pull and bind between the legs and are generally tight feeling and restricting across the stomach and upper thighs.  Don’t worry, this fit issue can be overcome!  Here is how:

With the muslin still on the wearer, cut a horizontal line through the center front of the crotch.  The fabric will release the tension and you will be left with a smile shaped gap.  Measure the widest point on this gap – this is the total amount you will need to add to the crotch seam so that there will no longer be strain lines.

There are two common pattern alterations that you can try to add this measurement to the crotch seam.  The first common and quick fix to try is to simply lengthen the crotch depth by slashing across the pants front at the hip and adding the appropriate amount of length.  This simple pattern alteration maintains the shape of the crotch curve but just makes it a little longer.

If you try this pattern alteration and it does not seem to work for you (for instance, your new muslin now looks like you are wearing drop crotch pants!), this is likely because the fit problem isn’t about the crotch depth being to short for you.  Instead, the problem is that the crotch circumference is too narrow and the seat seam curve does not suit the shape of your body.  This may be because your abdomen is slightly more rounded than the fit model’s shape or it could be due to roundness in the crotch caused by specifically male body parts!  Either way, you will need to perform a slightly more complicated alteration to your pants front pattern piece.

Here is how to add crotch circumference: 

1. Mark all the seamlines on your pants front pattern piece.  The seam allowance included within the Jedediah Pants and Jutland Pants patterns in 5/8″.  When performing alterations to a pattern piece you need to work from the seamline (where you will actually be sewing) rather than from the edge of the pattern piece so that you will retain the original shape of the pattern.

2.  Draw a horizontal line across the hips of the pant front pattern piece.  Slash along that line from the fly front to just before the side seamline – don’t cut all the way through the seamline and seam allowance because you will need to leave a little bit of paper here to act as a hinge.  Now cut into the seam allowance without removing that tiny paper hinge.

3. Draw a line from the inseam seamline at knee level up to the crotch seam.  Try to end your line somewhere before the fly extension curve.  Cut from the crotch seam down to the inseam at knee level and again leave a little hinge of paper at the seamline.  Cut into the seam allowance on a diagonal without removing that tiny paper hinge.

4. Spread the two slashes slightly so that the crotch seam extends to the left and the waistline swings upwards.  You will notice that the little clips you made into the seam allowance will allow the seam allowance to overlap as you spread the pattern.  When measuring along the seamline (not the edge of the pattern piece), the total size of your two gaps should equal the measurement that you found when you cut across your first muslin.

5. Secure your spread pattern piece in place by taping the pattern to a couple new sheets of tissue paper.  Smooth the curve along the crotch seamline and smooth the seam allowance to match.

 

6. Depending on the pattern you are using, you will likely need to adjust a number of other small pattern pieces to suit the changes you made.  These will likely include the pocket pieces and facings and the fly shield.  The easiest way to make these changes is to line up the paper pattern pieces underneath the pants front pattern and trace the new angles onto the pocket.  Lengthen the fly shield to match the new length of the fly facing.

 

*** If you are experiencing lines radiating from center back across the bottom and the pants seat seems generally too tight and flat for the rounded shape of your body, the same alteration can be applied to the pants back.  Slash and spread along several points at center back – try to pick points along the seat seam where the seam seems to least match your body.