How to use formulas in curves for Bra's

Kromming van AVC14 naar AVC12 via AVC1 en hendelspositie

Ik werk nu geruime tijd met Seamly2D maar het volgende is mij nog niet gelukt. De afbeeldingen zijn van alleen voorcup van een BH. Welke formule moet ik gebruiken om deze krommingen te krijgen zodat deze mee veranderen als ik een andere BH maat gebruik? En dat de krommingen van de kleinste maat in verhouding gelijkwaardig zijn aan de grootste maat. Het is belangrijk voor het patroon dat kromming AVC12 naar AVC6 een bepaalde lengte heeft als onderdeel van de gehele beugellijn lengte. Wie kan mij helpen. Ik ben helaas niet echt wiskundig aangelegd.

Alvast heel erg bedankt

I have been working with Seamly2D for quite some time now, but I have not succeeded in the following. The images are from front cup only of a bra. Which formula should I use to get these curves so that they change when I use a different bra size? And that the curvatures of the smallest size are proportionally equivalent to the largest size. It is important to the pattern that curvature AVC12 to AVC6 has a certain length as part of the entire stirrup line length. Who can help me. Unfortunately, I am not really mathematic.

Thank you very much in advance Esther Dekker

Superb question! Can you upload the files? It would be difficult to say without knowing the current measurements and formulas.

1 Like

Basic pattern bra size 80B (dutch).val (10.4 KB)


Hi slspencer,

Dank u voor uw snelle reactie. Ik heb dit nooit eerder gedaan dus ik hoop dat ik goed doe. Ik heb in deze patroontekening 2 krommingen getekend:

  • AVC1a-AVC12: deze lijn moet lijn AVC3-AVC5 raken maar dan onder het punt AVC1. Hier is de lengte niet erg van belang. Het begin en het eind van deze kromming moet als het ware een verlenging zijn van hulplijnen
  • AVC12-AVC6: deze lijn is onderdeel van de beugellijn lengte. Die staat voor elke BH maat vast. De gehele beugellijn bestaat uit de volgende lijnen (AVC12-AVC6) + (AVC13-AVC7-AVC8). Er staan nu geen formules bij de hendels van deze krommingen omdat ik niet weet hoe ik dat het beste kan aanpakken. De vertaling komt van google translate.

Thank you very much for your quick response. I have never done this before so I hope I have done it right. I have drawn 2 curves in this pattern drawing:

  • AVC1a-AVC12: this line must touch line AVC3-AVC5 but under point AVC1. The length is not very important here. The beginning and the end of this curve must, if possible, be an extension of auxiliary lines
  • AVC12-AVC6: This line is part of the underwire line length. This is a fixed length for every bra size. The entire length of the underwire line consists of the following lines (AVC12-AVC6) + (AVC13-AVC7-AVC8). There are no formulas on the handles of these curves now because I don’t know how to do that. The translation is duthch-english is done through google translate. I hope you can help me.

Thank you very much.

Esther Dekker

Hi @freelancer, @slspencer will need the measurements file (.vit) as well :slight_smile:

O I am sorry. Didn’t think of that. Silly me. :woozy_face:

Here is the file for 80B.

Confectiemaat 80B.vit (840 Bytes)


Hi again, @freelancer

@slspencer is the best person to help you with this that I know of. Unfortunately, she’s really busy at this time with the program, so I’m going to try and head you in the right direction with the way that I would do it.

The secret of getting the curves to resize is with using formulas that reference the angle and length of lines in the pattern. These lines should preferably reference a measurement in the .vit file.

Once you have the reference line or angle in then you can start playing with percentages as I have done here:

To create a perfect curve would be to make the handle 55% long, so I start with adding * 0.55 to the end of my formula and then increase this or decrease it until it looks right.

As for the angle, you will see that I added a line from AVC5 to AVC12 (I had to do this back in the History since you’d already duplicated the left side on the right side, but this is a whole new topic that you can read up on). I used this as the angle of the handle in the curve at node AVC12 and then subtracted 10 degrees off it to get the curve to follow the curve of the arc.

The handle at AVC6, I referenced a line that goes at 270 degrees to have the curve going smoothly into the line AVC7 to AVC8 on the right side, and then I made the handle quite short so that it starts curving quite soon to keep a nice shape.

I did the same with the other curve:

I can’t test the resizing but this should resize very nicely when you change the measurements file. Please let me know how it resizes :smile:

Here is your pattern file back, that I have made the changes on, so that you can see what I’ve done: Basic pattern bra size 80B (dutch)_a.val (10.5 KB) - You may have to point the pattern back to your measurements file when you open it the 1st time.


Hi again Grace,

Thank you very much for answering my question. I’m going to delve into this and see how this works for me. Thank you very much. You’ll hear from me as soon I tried this on the other measurments.


Hi Grace, I used the formulas you gave me. I have left out the formulas that have been used for the cups (bust), as there are no fixed lengths. However, the AVC6-AVC12 and AVC7-AVC13 do. And I tested it with all cup sizes. Fine tuning becomes monk’s work I already know. As the cup sizes increase, the curvature lengths also deviate. Although mm, but that is very important for a bra. I think I should start making smaller nests. But for the time being, the formulas are working pretty well. Thank you for that. Greetings Esther

This text is translate with google translate, so probably not the best english.

1 Like

Hi @freelancer,

Thank you very much :slight_smile: I also use google translate a lot. However, the internet is a wonderful place. If you right-click on the page, there is a menu that pops up that gives you the option to translate the page, which makes me really lazy. :star_struck:


There are a few very good topics on the forum about making curves and this one is one of my favourites that got me creating curves nicely: Another "very mathematical" way of making curves!.

And then here is a very nice tutorial on bra pattern making, that may interest you, where @AVI has given the formulas for the curves: Kristina Shin Basic underwire bra tutorial.

I hope that this will help you to understand the process a bit better to create your curves smoothly and easily. :slight_smile: