"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,

1. 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)
2. then measure from the red dot down your back to your waistline = B; (this is the red line)
3. 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:

The difference between my front measurement and my back measurement is about 2 cm (halved to 1 cm for the split triangle), and the side dart length is about 13 cm on me.

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.

1. 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). 
2. 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

How to do a Small Bust Adjustment (SBA) on Your Metric Pattern Cutting Close Fitting Block/Sloper

I have been scouring the web the past few days, and looking in my sewing and pattern making books for how to do a small bust adjustment, but none of the tutorials helped very much. So I figured it out myself, and it's so easy (now)!

So I thought I'd do a tutorial for other slim sewists, especially those of you who use Metric Pattern Cutting for Womens Wear by Winifred Aldrich.

Benefits of this SBA Method

• This method does not require you to cut up your original pattern, so if you have to do it again, you don't have to redraft your sloper. It uses the pivot and trace method of pattern making and can be done in a matter of minutes.
• It also does not affect the bust measurement of your pattern, so if you have the right width and the the correct amount of ease, you will maintain that, and simply reduce the cup size!
• Neither does it alter the waistline in anyway. All the alteration is done in the top of the bodice, so it's great if you have a good fit otherwise on your one-piece dress block.

I will mention ahead of time though, that this method works best if you use a master pattern and develop your designs from that. I don't really know how to alter patterns using a master pattern.

How to Do a SBA (Small Bust Adjustment) The Quick, Easy, and Sensible Way

You will require your sloper to have the bust dart in it's original position at the neck point.

1. Lay some tracing paper over your front sloper (I'm using Burda Tracing Tissue Paper) and weight it down. Here I have drawn over the original sloper on Microsoft Paint because it was hard to see in the photograph.

2. Starting at the bust point, trace the sloper up to the neck point, along the neck line, down the centre front, along the waist line including the dart, and up the side seam, stopping at the armhole point.

Mark a line at the top of the pattern 1cm down from the neck point and perpendicular to the CF. 1cm is the amount we will be reducing the pattern's length. Don't worry about the neckline; that will be sorted out later.

3. Put a pin in the pivot point and, with the tracing paper stationary (pun intended), swivel the original pattern underneath until the neck point on the shoulder line meets the line you drew in step 2.

Continue tracing your sloper, around the armscye and along the shoulder line.

When you get to the pink line in this photo, take your ruler and draw a line from the shoulder-neck point where you are, to the original bust point.

4. Lower the neckline at the shoulder point to the line you drew in step 2, and at the CF by 1cm to match. Redraw the neckline curve (or shift the tracing paper up 1cm and trace it.

The red lines in this photo are the new pattern, and the black lines are the original pattern. See how much narrower the dart is? That's the difference between cup sizes, that and the pattern's front length. We slimmer sewists simply don't need all that extra fabric.

You will be delighted with the difference this one, quick, simple alteration makes to your finished garments! Do this alteration before you do any others, then do any other length alterations, then width alterations. I speak from personal experience here. If your bodice is too short above the waist, it will look like the waistline is miles too big. Lower it to its proper place and voilá! Like magic it looks so much better!

So that is my method for how to do a small bust adjustment on your Metric Pattern Cutting Close Fitting Block/Sloper. It wasn't mentioned in Winifred Aldrich's book, so here is is for you. I hope it helps you as much as it will help me. Isn't it exciting to think you have a master pattern that fits and you can develop any design from it? : D

Until next time, happy sewing and pattern making!

Sabrina Wharton-Brown

The Sewing Corner

P.S. In case you wondered what I got for my birthday, I got Threads DVD-ROM Archive 1985-2011 (lots of great information once Mum got it to work for me on the computer) and the free book (FAST FIT by Sandra Betzina) which was on offer with it. My brother also got me The Magic by Rhonda Byrne of The Secret. He search Hull for it. Isn't he thoughtful? : ) It's a great book and I recommend it so far. It's certainly a pick-me-up.