Everyone has alterations to make of some kind, but observing fabric on the body is the key to making the correct ones. Here are a few words about how to understand alterations and interpret fabric behaviour.
You will need to pay close attention to the lines and folds of your fabric when you try on your toile or test garment.
[N.B. This is an expanded version of an earlier post in March 2024. I decided it needed an update in late 2025, and it was big enough to warrant republishing!]
The language of fabric
There are two main types of alteration: two-dimensional (2D), which represents length and width; and three-dimensional (3D), which represents volume.
2D alterations
- Any alteration that involves horizontal or vertical lines is 2D, and you will need to either lengthen or shorten your pattern to achieve the right LENGTH; or narrow or widen to achieve the right WIDTH.
- The consistent horizontal or vertical lines of 2D alterations indicate a consistent shape at that location on the body, with no changes in volume.
3D alterations
- Any alteration that involves diagonal lines is 3D, and you will need to either increase or decrease the volume afforded by your pattern.
- Volume is represented by CONTOURS or FULLNESS. The areas that needs fitting will not be flat, regardless of whether you need to increase or decrease volume.
- Design features that accommodate volume include darts, pleats, and gathers. You will need to alter or create these so that they take in more or less fabric.
Fabric behaviour: Analysing the lines created by the fabric on your body
Diagonal lines have a couple of variations. They may be radial, or form drag lines/dart folds forming around the bust point or apex. They can also form a horizontal wedge, which may take the form of a double-ended dart (e.g., centre back seam, tapering to nothing at the side seams). Both diagonal lines indicate a need to increase or decrease fabric somewhere: note how the dart is formed as you pin and fit. The dart tip will point to the fullest area; the distance between the dart legs will reveal the amount of SUPPRESSION or volume reduction needed.
On the other hand, horizontal or vertical lines represent straightforward changes to length or width respectively.
| Profile of line | Adjustment indicated | Drag lines? (Fabric strain) | Fold lines? (Fabric excess) | 2D or 3D? |
| Horizontal | Length | Increase length | Decrease length | 2D |
| Vertical | Width | Increase width | Decrease width | 2D |
| Diagonal | Volume or curvature | Increase volume | Decrease volume | 3D |
Examples of fabric line profiles for bodice alterations | A personal case study
The photos here are of me in a RTW linen dress. You can see that a diagonal line has formed at the waist seam of the bodice. At the centre back, there is too much fabric – evidenced by the sagging pouch, which gets deeper at my spinal column. Conversely, at the centre front, the fabric rides too high, indicating strain and not enough length. To alter this so that it lies straight on my body and parallel to my contours, I need a curved waist seam. Further proof of this can be seen in my bespoke bodice blocks below.
Use your bespoke blocks to support you when altering commercial patterns
It can be unnerving to come to conclusions like this when you are making clothes alone. You can’t confer with anyone who’s had the same experience. This empathy (or lack thereof) isn’t great for confidence.
This is another reason why I recommend drafting your personal blocks. They offer you a helpful target when altering commercial patterns. If you’ve already fitted something to your shape, it’s MUCH easier for you to evaluate a new pattern. You’ll see what you need to do and develop analytical and forensic skills to be able to tackle any pattern.
Fabric behaviour | Alterations for knits and wovens
Knitted (or stretch) and woven fabric behaves in much the same way when giving you clues about the type of alteration you need to make. The main difference is that the stretchiness of knits can mask alterations. What feels uncomfortable or shows up in woven fabrics can feel and look okay in knits. Fabrication doesn’t solve the problem – but puts you on parole, if that makes sense! Some sewists avoid making alterations by sticking to knit fabrics, but that won’t work for everyone. Altering patterns correctly puts less strain on the fabric, and adds longevity to your clothes.
The same applies to handknits and crochet, but the delicacy of handmade fabrics should also be considered. The larger gauge (compared to machine knits) and versatility of stitchwork neutralises any benefits of stretch. Recovery – or a fabric’s ability to return to its original dimensions after being stretched – is often poorer. This mechanical recovery is something to consider alongside fibre type. Protein fibres, e.g., wool, have better recovery than cellulosic, e.g., cotton, but this usually just buys you more time. I’ve found that it’s best to treat handknitted and crochet garment alterations in the same way as woven fabrics, letting the pattern do the heavy lifting, not the fabric.
Wrapping up
I hope these tips on alterations and fabric behaviour are helpful! Observing fabric behaviour is key to correctly identifying the alterations you need to make. If this advice was useful, please feel free to bookmark or pin this post, or share it with a clothes maker you know. And if you’d like more content like this, leave a comment below or sign up for my weekly newsletter, Between the Seams.
This is also my final post of the season, so I’ll see you in 2025! Please comment below if there’s anything you’d like to see more (or less) of on the blog. It remains for me to thank Connie and Katie for their support via Ko-Fi – and if you’re in a generous mood, my tip jar is to the bottom left of your screen. Thank you 🙂