How to measure your body to see if you need bust darts

If you are a busty person, then you may have experienced some unpleasant side effects while garment knitting. You may have experienced a lot of riding up on the front (see this poor dress form below), a frown downturned shape on the style lines and visual features of your sweater.

Yes, you can yank it right back into place, but our bodies are fluid, and 3D, and throughout the day as you move around, the fabric will continually want to do the things it wants to do and move to unstretch and cover that area better. 

These days, cropped sweaters and tops are popular, and you may have been burned by them being too cropped in the front, or been hesitate to knit one at all. 

If you've had any of these things happen to you, you might need horizontal bust darts. You can see in this above photo that this dress form REALLY needs a little something extra--the tilt of the hem line AND the style lines (the purl rows) are a dead giveaway. 

Because boobs are 3D, sometimes adding width in the area is not sufficient to give you the coverage you need. And worse, if you're knitting a larger size just to accommodate the bust tissue, you'll end up with a baggy fit everywhere else. While all our latest patterns made for a women's size chart have a wider front than back to accommodate bust tissue, sometimes you just need a little more. 

In all my adult garments since 2022, I've included additional bust cup sizes, otherwise known as optional bust darts, to give room in the front for those who have need for it. However, we get a lot of questions on how you can measure for them. 

As a side note: Almost all the sweater styles I design benefit from bust darts, but fitted styles show fit problems particularly.

You can see above this negative ease garment really rides up because there's not enough vertical fabric to cover the bust tissue this dress form has! Additionally, the purl rows, a decorative style line, is bowing out in a way that it doesn't on straight sized people who don't need bust darts.

You may not have noticed this problem until your first fitted top, but here's how you can measure to empirically work out how much you need to add to resolve this issue. 

By the end of this post, you'll know how to quantify your bust tissue differences from a standard size chart "sewing B cup" so you can knit a better fit. 

Disclaimer: This method is not suitable for sewers, because knitting stretches and this method accounts for the stretch in the fabric! It may give you information on whether you need to do an FBA (full bust adjustment) in sewing or not, but will not give you information on how much to add. 

If you are not familiar with horizontal bust darts in knitting, which is our equivalent of a Full Bust Adjustment (in sewing), or you'd like to see this on a real person, you can check out a case study on Sara, a test knitter who generously shared her before/after with us! 

Horizontal bust darts will add a wedge of fabric where you need more coverage, which brings the "grainline"—in our case, the knitted row, level below that point of fullness. I've roughly sketched it out on Mia below so you can see where her bust darts are. 

Tools for measuring horizontal bust darts

You will need: 

• A well-fitting bra or an elastic you can tie around your underbust 
  
• A soft (not rigid) measuring tape 
• Any under layers you are planning to wear under the garment/pattern you are making, such as a bra or any shapewear
• The hardest part...a friend or second pair of hands to help you with the measurements

It is is critical that you wear the foundation garments you mean to wear with the finished product. You need to do so during the measurement stages and any trying on stages, so you can assess the fit only when you are wearing them, which keeps your fitting notes consistent. 

Additionally, you will absolutely need a second pair of hands, or a friend/spouse/roommate/whoever to help you with this. Twisting around yourself to get the measurement will cause errors are our bodies shift and change in movements like that and you won't get an accurate read. 

Setting up 

First, you'll need to put on your well-fitting bra. You can do it over a cami or tightly fitted tee if you have a friend over to help, or tie an elastic (1/4" inch, 1/2" inch...whatever works) around your underbust where the bra band usually sits, over all your foundation garments (bras, shapewear, etc, as previously mentioned). 

Make sure that this elastic line is parallel to the floor all the way around.

Another way that my customers have had success with is using washi tape over a light jersey cami to mark the spot all the way around.

You'll be using this line as a reference point to measure your front and back lengths from the shoulder to this point, to understand how much bust tissue you need to account for in horizontal bust darts. 

Measuring the back for a baseline 

From your shoulder point, which is typically under the middle of your ear and where the seam of a well-fitting tshirt would go (excluding raglan constructions), measure down perpendicular to the ground and to your fitting elastic, for the distance on the back. Write this down. 

For this measurement, I like to do it in the mid-shoulder, where the bra strap will sit, because further up, people who work out or have a particularly strong "trap" muscle structure will often not have the same amount of tissue front and back there, and we are measuring for consistency. 

Additionally, if you have a muscular back from exercise (I see this most often in ballet dancers, rock climbers, and power lifters), you'll need to mentally account for that and subtract that from what you measure. If you have a full, rounded back due to age or slouching, then you'll also have to account for that separately before you address bust darts (a subject for another post, I think). 

My dress form is about 12" down the back. 

Measuring the front

Repeat this measurement on the front of the body, still making sure to keep perpendicular to the floor, from the mid-shoulder. If your garment is fitted, then hold the tape to the contour of the breast tissue and bra cup (if you are wearing one). My dress form measures 16" here. 

Measuring the front in oversized garments 

If your garment is going to hang straight over your bust tissue without contouring under it, such as in an oversized garment, you won't need as much bust dart coverage as you would in a fitted garment. You would then need to eyeball this figure with the tape hanging off the fullest part of the breast, like this: 

Calculating for bust darts 

Subtract your back length measurement from your front-length measurement, and that's how much bust tissue you have vertically! 

On my dress form, this number is 4". 

Because knitting stretches, the fabric stretch itself automatically accommodate 2" easily, so you'll subtract 2" from your measurement, coming to 2." To knit a shirt that will fit my dress form as shown here, you'll need to add 2" in length in bust darts. 

If you are in between whole numbers, or you are unsure you measured accurately, size down 1". It's better to have slightly too few rows than too many. 

My patterns from 2022 on all have these bonus cup sizes built in, so you can check our Garments with Bust Darts page out if this is something you have a need for! 

Bust dart placement for the apex 

From time to time, I have a knitter who has wide set breasts or closer set breasts, who needs to modify the bust darts further. It's pretty hard to know it before you make it (which is why in sewing we make mock ups!), but when you encounter this problem you'll know this is the measurement to correct. 

The apex is the tip of the projection of the fullness of your breast. This may not necessarily be the nipple, on most people. You will need to look at yourself sideways in a mirror to mark this spot. 

Another way that sounds silly is to walk breasts first straight into a wall. Your apexes will be the first thing that touches the wall. 

Once you find out your apex placements, you'll want to make sure the start and end of the bust dart turns are placed outside of these points. Typically you'll want to see them 3/4" of an inch to the outside of these points. 

This means that you may need to adjust where you place the darts height wise too, as you want the darts to point right at the apex to target that fullness where you need it. 

That's about it! 

That's all I have for you today. I hope that this was helpful to you and that you can go forth and measure yourself with no fear, and enjoy your beautifully well fitting finished garment soon. 

Other articles about fit you might like: 

• All about compound raglan construction
• How to choose a size in knitting
• Measuring your armhole depth
• Raglan depth and armhole depth: what's the difference?  

... and more, at our Knitting Resources page.