Crotch Curve Adjustment - The Tin Foil Method

“I like big butts and I cannot lie!”

You know the rest. I really do love my unique and rather large derriere. But it can make sewing pants that fit a bit tricky, and don’t even get me started on buying pants to fit, that is never going to happen. I have learned over the years that I can have pants that fit, I just have to alter most patterns to fit my unique, amazing booty. My favorite way to make a crotch curve adjustment is using the Foil Method. So grab some tin foil and I will teach you how to get the best fitting pants money can’t buy!

Tin Foil Method

Drafting the Adjustment


Step 1:

Lay your foil out so it is long enough to cover the length of your crotch curve. Then fold or squish it up “hotdog style” so it looks like a long foil snake. (If you have a flex ruler you won’t need the tin foil snake).

Step 2:

Wrap the rubber band or place the clip in the middle of the foil, we will move it in a later step.

Step 3:

This is where things get a little personal. With some leggings or tight-fitting pants on, place the foil between your legs and move the rubber band to where the inseams are attached (the center point of your crotch).

Step 4:

Forgive me, but you cannot get a flattering picture of wrapping up your own crotch. It’s impossible. I did my best.

Shape the foil or ruler to the curve of your crotch. We want the impression to go from the front just above the front of your pelvis all the way to the back top of your butt. Make sure to get a good impression of your butt during this process.

As you do this you will want to form the foil comfortably around your body. It should not be recessed into your vulva or butt cheeks.



Step 5:

Very carefully, like a ninja, step out of your foil crotch. Try not to move it around or fiddle with it. The best way to do this is with a helping hand. Have someone else handle the foil while you step out. We don’t want to ruin the curve we just created. If you don’t have an assistant you can just slowly drop it to the floor.

Step 6:

Transfer your foil, by laying it on a piece of paper and trace the whole curve. Mark where the inseam is placed (where you placed your rubberband/clip). Also, mark which side is the front of the crotch and which side is the back.

Crotch Curve Adjustment

Marvel at your crotch curve. For me, mine is very different then what most pants are drafted for. Which is why literally no ready to wear pants fit me correctly.

Now grab your ABB Leggings and let’s see how we can use our curve to modify the pattern to get the perfect fit.

Modifying Your Pattern

We are going to need a front and back piece. Prepare your pattern according to the pattern’s instructions (i.e. size blending/grading and height adjusting) and trace it on tissue paper or butcher paper. It’s always best to make messy adjustments to a copy then transfer them back to your Master copy once you’ve nailed them.

First, we need to see the pattern’s original crotch curve. Do this by lining the inseam up, don’t worry about lining the legs up. Since the seam allowance for these pants is 3/8 of an inch we are going to overlap them to account for that. Just use a small piece of tape so you can easily separate the pieces later.

Match the inseam of your crotch curve to the inseam of the pants.

Tip: Try to position the base of your crotch curve so it is relatively flat/smooth going up on both sides.

Crotch Curve Adjustment Perfect Fit


Now if this is your first time doing this and you have curves similar to mine you might be in a little shock right now. “How on Earth can I make these pants fit me?” Deep breath, I got you.

The first thing to remember is that there are many other alterations that we can use to adjust for significant differences between our bodies and the pattern. In the example above, the experienced sewist will notice that I will need a swayback adjustment (my booty is poppin and it comes back in sharply). This is something that I will adjust for at another time.

For now, I need you to remember that pattern alterations are often an art form rather than a science. We will be mimicking the original pattern as much as possible while considering my body’s unique crotch curve. Let me show you how.

Take a look at the image below. I drew my unique crotch curve (in orange) over the pattern’s original crotch curve (in blue) as a guideline.

The green line is my new crotch curve. In the front, I chose not to take such a large amount off and cut my adjustment in half. For the back, I used the original top point and came out to my crotch curve’s most outward point. I tried to keep a similar shape to the curve as the original’s.

Crotch Curve Adjustment

You can tell just from the picture that I have a big butt. On knit pants, such as leggings I tend to get a wedgie. I also have a protruding pubis which often gives me a small camel toe. TMI sorry, but it’s ok we are fixing these problems. Both of these things are not flattering at all, and make for an uncomfortable pulling at my clothing type of day.

We’re Not Done Yet!

Please, please, please do not forget this step! As you change the curve of the pants by either adding to the curve or taking some away, it must be adjusted at the outer seam so the pants can fit. For example: If I cut off 1″ from my crotch curve that takes away 1″ of fabric from my pants. So without adding that 1″ back in they will be 2″ too tight (1″ off from each leg). You don’t want that.

I took away from the curve, which most people will tend to do. All I have to do at this point is to add it back to the outseam. It looks wonky on my two-dimensional pattern but when it’s put onto my three-dimensional body, it will be fabulous.

Back Leg Crotch Curve Adjustment

Front Leg Crotch Curve Adjustment

Then just sew them up per the pattern instructions.

Crotch Curve Adjustment Final

Crotch Curve Adjustment Final

What do you think? Do you have the same curve as ready to wear clothing? Is it all over the place and you’re thinking to yourself, “no wonder my pants fit weird”. Maybe you have a flatter booty, a rounder booty, a full tummy, or a hip tilt. No matter what your unique shape is, you can make your pants fit you better than anything you could ever buy!

This method can be used on most pants patterns. Knits are the easiest to alter because they have some stretch to them but woven patterns like our amazing jeans can also be altered using the tin foil method.

No pattern is set in stone. The beauty of sewing your own clothing is that every pattern can be changed and altered to fit your body. We can all have clothing that fits each of our unique bodies.

If you like this article, check out our free eBook: Custom Fit Your Jeans. You'll learn all the common alterations and pattern adjustments you will need to achieve the perfect fit!

-- Originally written by Nicole Cook. Archived by Holly Hetzner

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