"How to Calculate Your Bust Dart Size: The Formula that Takes the Guess-work out of FBAs and SBAs"
When you look in Pattern-making books they usually have a table of standard measurements including either the bust dart width, or it's angle in degrees. These "standard measurements" are for a B-cup, which means that if you are not a B-cup, you have to draft the pattern and then do either a Small Bust Adjustment or a Full Bust Adjustment.
But how do they get these numbers? They seem to have nothing to do with the rest of the measurements. But there is always a formula. It just takes a bit of working out.
What is a bust dart's function? As I see it, a bust dart is there to make the longer front pattern piece match the shorter back pattern piece at the side seam. The front pattern piece is longer than the back one because it has your bust to go over and the back doesn't.
So to find out the bust dart's width at the side seam,
- you measure your front from the neck point the red dot over the apex (the green dot on the drawing), and thence straight down to your waistline = F; (this measurement is the orange line in the picture)
- then measure from the red dot down your back to your waistline = B; (this is the red line)
- subtract B from F and you have your bust dart width, which is the difference between your front bodice length, and your back bodice length.
Now for a little trigonometry. Scientific calculators at the ready!
We'll split the bust dart into two equal parts so that we have two right angle triangles:
How to Find Your Bust Dart Angle for Patternmaking in Fashion
If you are using the German method of pattern making, which is briefly taught in Patternmaking in Fashion by Lucia Mors de Castro (mine cost about £40 but it now costs £100 at Amazon due to high demand - I think it is over-priced now by very greedy sellers), you will need the angle of the bust dart, and as we have the length of the dart (the hypotenuse) and the width of the dart (the length "opposite" the angle) we can find the Sine of the angle (sin = O/h) and then use the sin-1 function on our scientific calculators to find the angle. Thus:-
How to Find Your Bust Dart Width for Metric Pattern Cutting
If you are using Metric Pattern Cutting for Women's Wear by Winifred Aldrich, or the instructions on www.BurdaStyle.com, you will want to find the bust dart width for a shoulder dart.
- Take the sine you found earlier (here 0.077) and multiply it by your neck to apex measurement (on me about 24 cm) to get half your total bust dart width. (Here, about 1.84 cm).
- Get your total bust dart width by doubling this number = 3.68 cm, roughly 3.7 cm.
So that is my bust dart: 3.7 cm wide at the neck point and 8.8 degrees (which can be rounded to 9 degrees for practical reasons).
So that is how you work out your personal bust dart measurement. Isn't it so much better than using a "standard" measurement?
I hope it helps. : )
Sabrina
Labels: Bust Dart, patternmaking
posted by SWB @ October 29, 2012
25 Comments
25 Comments:
Thank you, this helps a lot.
Hi Ms. Wharton-Brown,
Here is a tutorial that may supplement your wonderful article. Please check it out.
Thank you.
http://kosherpatterns.com/tutorials2/24-how-to-add-a-bust-dart-to-a-dartless-pattern.html
hi, my name is Prime. Ur article was really helpful. Two questions please: how did u get the first length of the bust dart?, and what did u mean when u said only half, that is 4.4 in ur case would be used? (the mention of 8.8 later for the got me a bit confused too)
#for the shoulder dart#
The length of the first bust dart is the distance from where your side seam would be (you can guess this by where it feels right) to the bust point.
About the "half": the bust dart is a triangle, and if you divide it down the middle, halving it, you get two right-angle triangles which are much easier to work with mathematically.
Because we divided the bust dart in two (so that we could use a right-angle triangle) the angle measurements and the length of the side marked "opposite" in the picture, are half what they would be for a full bust dart. That is why the 4.4º gets doubled to make 8.8º.
The 4.4º comes about from having your scientific calculator do some backward trigonometry. If you type in "Sinˆ-1 0.077 =" on your scientific calculator it will give you the number 4.4.
Thank you for commenting. I thought I had added more images to this post than I had, so I'll add them now, and that should help to illustrate the information.
The shoulder dart is the Metric Pattern Cutting one.
Thank you so much for this tutorial
Thank you very much for share this method. Greetings from Chile.
So I have a silly question. Why do we need the angle if we already have the length and width of the dart?
Hi Saleen,
Good question! You need the angle because we're not drafting the pattern with a side dart, so we can't just pivot it. I suppose you could adapt the pattern cutting method to start with a side dart, but I'm keeping to Aldrich's basic method because it's what I'm used to and have instructions for. :) Working out the angle means you can work out the width as it will be at the neck-shoulder point, which is naturally more than it would be on a side dart (which is shorter).
Hope that helps! :)
Hey,
Fellow design student from Denmark here,
Since I have been teached with Metric Pattern cutting for womens wear by W. Aldrich, and thereby never formerly learned about Darts, it would be highly interesting to know how to make them for pants.
As far as I understand it, one should be able to apply the same technique you explained above but measuring from the waist point down to under the hip line on both front and back, subtracting the two for the width but then again, with pants the dart width is more dictated by the way of construction and how many cm/inch were added in the waist during construction and now need to be taken out to fit the waist properly.
But that does not really help with the question of the darts length…
The book Fashion Patternmaking Techniques vol. 1 by Antonio Donnanno kind of explains bust darts with saying that, depending on the radius of the bust circle (3.5-5cm) that would dictate the length, but could one just go ahead and apply the theory of the bust circle onto the back hip area and thereby figure out the darts length?
I hope I have not confused to much with my kind of rambling form of writing and my general problem and thought still got across.
Maybe I am even totally wrong with my thought process here and there is a whole nother way of constructing darts for pants.
Best Regards
Hello!
I'm sorry this is about 9 months late but I just saw your comment!
I agree, and it's a very good idea to use this sort of maths for skirt/trouser darts too. For the length I would just measure on the person/dress form.
I haven't tried it. Have you since you wrote your message? For bottom garments I use different maths, which you can find on the post about how to draft an a-line skirt block. :)
Pls can this be used for the shoulder dart as well
Hi! I only just got the notification of your comment! :) If you follow the steps through to the end, you get the shoulder bust dart measurement. Is that what you mean?
If you mean the back shoulder dart, I haven't tried to work that out. :)
Hi. This method sounds good. But it works when the front bodice length is longer than the back. For a person with a hunched back where both the lengths are the same or the back length is a big longer. What does one do then?
Awaiting your response.
Thankyou
Hi!
I *think* you would have to measure a straight line down from the person's side shoulder point, but with the tape measure in the air, rather than laying against them. It might take two people and a set square against the wall to measure it (to keep things level), but that's the solution that comes to my mind.
If they had a really hunched back, it might be possible to calculate the shoulder dart in a similar way. I'd have to test it, but I don't live near anyone with a hunched back.
Okay let's ignore the hunched back for a moment here. But in a situation where both the front length and back length are similiar or the back length is longer. Would this method still work in calculating the bust dart size?
I don't think that person would need a bust dart as calculated here. I think in that case, a waist dart would be enough. You can see how I calculate those on this page: https://thesewingcorner.blogspot.com/2013/02/redrafting-my-sloper-or-updating-aldrich.html :)
Once you have worked out the Sine of Angle (sin=O/h), then enter the result into the top box of this calculator https://www.inchcalculator.com/inverse-sine-calculator/ to get the angle. Don't forget to multiply the angle by two!
If we do this dart, is drafting shoulder dart also necessary? Or we can do the slash and spread method to transfer this single dart to desired areas?
Also what is the location of this dart, is it on the bust-waist dart or the side bust dart?
This is for drafting the shoulder dart. The number you get at the end is used instead of the standard bust dart width used in Metric Pattern Cutting.
This is the bust dart. The bust-waist dart is drafted separately.
So it's on the shoulder to bust location is that right? Also do we need to draft any other dart or we can use split and spread method to transfer it to different areas?
That's right. You can split this dart if you wish, and if you want to add waist shaping, that will be drafted separately to the dart here.
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