Building better trousers with SCIENCE

I’m still very much in sewing mode rather than knitting mode these days. I’ve decided I need new work trousers and the only way forward is to sew them myself.

Unfortunately making trousers that fit well is a high-level challenge. All those intersecting topographies at the crotch! Once you’ve got that bit right the rest will follow. I’ve not found a satisfactory crotch-seam drafting tutorial on the internet and I’ve watched my own mum have limited success with the Palmer & Alto tissue-fitting method. Frankly, everyone seems to be relying on standard crotch seam templates and blind trial and error, which just isn’t good enough for a professional woman of science such as myself.

The best advice I ever got as a Physics undergraduate was this: YOU CAN SOLVE ANYTHING WITH LASERS


This is the Bosch PLR15 Laser Measure. It can measure distances to an accuracy of ±3 mm, which is the highest acceptable accuracy I was willing to pay for.

So what I did this weekend was measure the profile of my crotch to an accuracy of ±3 mm. Yes, I genuinely believe the findings are worth a blog post on their own! Let me detail the method: I marked up the centre of an A3 piece of paper with 1cm increments, and stood in my knickers with my feet either side of the paper, whilst my incredibly good-humoured boyfriend moved the laser measure along the marks, noting the distance measured. He also noted the ideal inseam placement.

So we ended up with a piece of paper like this:


Which I translated into the following x-z plot. Not well, mind you, I had to redraw a few points.


There’s some variation here, which we will have to chalk up to measurement uncertainties and also any movements I made whilst standing. Nonetheless I think it shows a fairly clear profile. Two things immediately jump out: the lowest part of the crotch is slightly behind the inseam, making it almost dead centre of the profile, and the front crotch is very long.


I then added error bars and a generously deep line of best fit. I had to think about that line. How closely should a crotch fit before it starts to highlight the er, “topography” a bit too well? I then cut the curve out of the paper and holding it against myself, the backside seemed to fit absolutely fine, but I had been skittish about the front and the resulting curve had too much depth. The overall length of the crotch profile was fairly spot on.

Compare the seams though, against the Palmer/Pleutsch trouser pattern, McCalls 6361.


The curve of my backside starts later, and is shallower than any of the suggested sewing lines the pattern has helpfully marked out. You can see my inseam marking through the paper here. It’s clear I really need to move the inseam if I’m going to make this pattern. The front crotch on the other hand…


Completely different to the pattern! Even moving the card back to compensate for hypothetical inseam movement, I can see that I need a very long front crotch. It explains a lot though. In shops, I always find trousers pull at the front crotch (the Palmer book calls them ‘smile lines’), or I get that oh-so-flattering camel toe, or both. At the back, I occasionally find some odd folding under the butt-cheeks but not very often. Incidentally I really hate shopping for trousers.

Redrafting the crotch seam to the extent I need it will take some doing, but hopefully my scientific hubris will pay off. At any rate, I feel like I’ve figured out an awful lot of trouser problems without doing any actual sewing.

Updates to follow when I have something wearable!


This post is dedicated to the lovely man in my life, and any other S.O. that, on hearing the question “Can you point this laser up my butt?”, says yes first, asks why second, and starts worrying about centering methods third.


Filed under Ramblings

10 responses to “Building better trousers with SCIENCE

  1. travelknitter

    This is brilliant. The best blog post title I’ve seen in a very long time!

  2. Q – Love this! Back in 1970 when I took Physics, my prof introduced the LASER and bore a hole through a cement block. He told us, “LASERS are only good to use as weapons!” HAHAHAHA. People without any vision. As a scientist, I love how your scientific brain came up with a wonderful solution to drafting the perfect trouser pattern!

    • Ha! Well I suppose the computing power wasn’t available back then. I just got thinking that we have plenty of 3D scanners these days, why couldn’t I just scan myself somehow?

      • Q – Great idea! If I scanned myself, I could have a copy do the housekeeping and cleaning, another could sew everything I want and a third could knit! Yeah!

        And, imagine taking physics and chemistry using a slide ruler! Hahah. TI had just come out with a hand-held calculator towards my last year in college. They were “illegal” since they were so expensive that most students could not afford them! Ah, memories.

  3. gilliancrafts

    This is brilliant! For those of us without lasers (WHY don’t I have a laser?) I’ve heard of molding a long wad of tin foil to match your crotch curve, or I’ve used this similar method with a flexible ruler:
    My own personal gripe about pants fitting suggestions online is that they all focus on big butts, but no one seems to have written much about big tummies and how to fit there. Come on people, help a girl out! 🙂

  4. Very interesting and funny 🙂
    Have you factored in sitting down? I don’t know how this changes any measurements, maybe not the crotch, but certainly the butt? I wouldn’t dare make trousers, but then I don’t wear them any more, because I don’t find them comfortable. Maybe if I could make some that fit perfectly? Who knows…

    • There’s so much to consider isn’t there! Sitting down shouldn’t change the crotch length, but it will pull down on the back waistline as the length of the butt muscles change. And your hips squish outwards as the front folds up… I think the fitting problems that occur in sitting are very similar to what you would find in a close fitting pencil skirt. I imagine the solution is the same in both cases – you don’t want the hip seams to fit too tightly, and a well-reinforced waistline is key.

      By the way I should probably mention I have never made trousers before! I may be talking out of my laserbutt.

      • I’ve not really made trousers as such, just some Anglo-Saxon ones which were a disaster as they split at the crotch when I fell over in the battle! Fortunately I was wearing something under them, plus the tunic goes over them to mid-thigh/knee level depending on how bloused you have it over a belt. That was over 20 years ago, well before the benefits of laser were generally available 🙂

  5. This is pure genius! All in the name of good fitting trousers. A worthy cause indeed.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s