Accommodate the bustline in your hand-knits
Updated: Oct 3, 2021
This article deals with the what, when, where, how and why of bust darts in hand-knitting. Sometimes you may not even need bust darts at all, even if you're a busty lady like me. The type of sweater you are making, the baseline chest measurement, the ease and your shape all play a part. Be prepared... all this makes for one long article. So I'll list the summary bullet points first and then go into detail.
What: There are both angled horizontal darts and vertical (think princess seams or Viennese shaping) darts. Horizontal darts are more common.
When: Use horizontal bust darts when the finished sweater would ride up in front. In some cases you may need to add additional width as well; vertical darts add width.
Where: One dart is created on each side of the sweater front. A horizontal dart starts no higher than the apex of the bust, and angles down from about 1" (or more) outside the nipple towards the side seam. Vertical princess darts begin at or slightly above the waist and flare out as additional stitches are added when knitting bottom-up.
How: Short-rows are used to create angled horizontal darts. Vertical darts are created by adding pairs of stitches to each dart on successive rows/rounds as the body of the sweater is being knitted from the bottom.
Why: Why do short-rows work? The short answer is that short-rows allow the circumference of the front to increase although the cross-section width does not change. Most of the time this is sufficient to accommodate the bust without either stretching the fabric or extra sagging.
When you are designing with KnitWiz, angled horizontal bust darts are included by default when necessary. Sometimes you may not want to include the short-rows; for example, the stitch pattern is complex and the angled line of short-rows will distort the pattern. When this is the case, you have the option of disabling the bust darts. Another option you may enable is the full-chest-baseline option. This option uses the full-chest measurement as the baseline chest measurement rather than the upper chest. Ease is then added to the full-chest measurement.
When are bust darts needed?
Measure around the fullest part of your chest. Then measure around the upper chest at the underarm. If the difference between the two measurements is greater than two inches (five centimeters), then consider adding horizontal darts.
Before knitting those darts think about the type of sleeve in your pattern. The fit of the
sleeve through the shoulder determines how your sweater will drape on the body. A dropped sleeve (basically a box) sweater has no shaping through the shoulder, and requires a significant amount of ease (at least seven to eight inches (18 to 21 cm)
through the chest to drape properly. Use the full-
chest measurement option for dropped-sleeve shaping, so that the bust does not cause the sweater to pull too much towards the front. Due to the boxy nature of a dropped sleeve garment, the bottom edge will naturally curve down towards the sides when worn. Since the bottom edge is curved anyway, bust darts are optional.
On the other hand, set in sleeves are shaped to conform to the contours of the shoulder and consequently fit the human body best. Horizontal bust darts are recommended for this style of sleeve. If you need darts and they are omitted, the result is a sweater which rides up in front. How far it rides up in front is the amount of extra length which needs to be added by using short-rows. (side note: I use usually add bust darts when making sweaters with modified drop sleeves, since I generally add less ease and want to avoid ride-up.)
Determine dart length
The difference between upper-chest and full-chest, less two inches (5cm) is an approximation often used to determine how much additional length needs to be provided by horizontal darts (i.e. short-rows). This is sufficient most of the time, and is currently how we calculate horizontal darts at KnitWiz. Side note: we are working to add an option to refine this calculation, which takes into account your "ride-up" measurement as described here. To determine exactly how much length to add with short rows measure from the top of your shoulder, over the fullest part of your bust, down to your natural waist. Then measure down the back from the top of the shoulder to the natural waist (you may need help from a friend for this one). The difference is the distance your sweater will ride up in front, your "ride-up" distance. This distance is also your dart length.
Bust Dart Placement
Imagine you are knitting a set in sleeve pullover with worsted weight yarn. Your stitch gauge is 20 stitches per 4" (10 cm) and your row gauge is 28 rows per 4" (10 cm). The pattern calls for 4" (10 cm) of ease at the upper chest. Let's assume your measurements match the figure above, so you'll need three inches (7.5 cm) extra length.
horizontal dart shaping on pullover, cardigan
Conventionally, set in sleeve patterns have between 1" (2.5 cm) and 1.5" (3.5 cm) ease at the underarm. Begin your darts three inches (7.5 cm) below the fullest point of your
bust. Typically, the fullest point of the bust is anywhere from one to three inches (2.5 - 7.5 cm) below the underarm. Let's say the fullest point is 2" (5 cm) below the underarm. Time for another measurement... measure from the top of your shoulder, down the front to your underarm. Let's say your shoulder-to-underarm measurement is 7" (18 cm). Now look at your finished pattern schematic and subtract 7" (18 cm) from the arm opening to get the underarm ease. If the schematic doesn't give this information, assume 1" (2.5 cm) of underarm ease.
KNITTING FROM THE BOTTOM
To create horizontal darts, you'll be adding short-rows. Your short-rows should end 1" (2.5 cm) below the armhole shaping, which means they begin 4" (10 cm) below the armhole shaping. You'll start the short-rows at the sides and work gradually towards the center.
KNITTING FROM THE TOP
When knitting down from the top, finish shaping your arm openings, knit one more inch (2.5 cm) and then begin short-row shaping working from the center out towards the sides.
Short-row Width Calculation
Before we can calculate how many stitches to work between short-rows, we need to calculate the width of the dart. Time for yet another measurement... measure the width distance between the fullest points of your bust (usually, but not always, the distance between the nipples) -- the 'fullBustWidth' measurement. Let's estimate this distance to be 8" (20 cm).
In this hypothetical scenario, the finished front width is 21" (53.5 cm). To determine the maximum dart width use the formula:
(frontSweaterWidth - fullBustWidth - 2"(5cm)) ÷ 2
(21 - 8 - 2) ÷ 2 = 5.5
You might be wondering why an additional two inches (5 cm) is subtracted in the formula. This is because the dart width should remain at least one inch outside the fullest point of the bust. With a row gauge of 7 rows/inch we need 21 rows, or ten sets of short-rows (rounding down). That means we need ten turns in 27 stitches (round down 5.5 x 5 stitchess/inch). Ten turns divides evenly into 27 two times; two stitches are available per turn. Translating into short-row instructions, this means one stitch is worked between each wrap and turn. If you were reading the instructions they would be written something like the following:
KNITTING FROM THE BOTTOM
" Work across front to 3 stitches from side marker, wrap & turn (w&t), work back across front to 3 stitches from side marker, w&t, work across to 2 stitches before previous turn, w&t on next stitch, rep. other side. Continue working short rows until all ten sets have been worked. Continue working in the round, picking up wrapped stitches when you come to them."
KNITTING FROM THE TOP
" Work across front to 20 stitches from side marker, wrap & turn (w&t), work back across front to 20 stitches from other side marker, w&t. *Work across to 1 stitch after previous turn, working the wrap in with the stitch as you come to it. On the next stitch, wrap and turn*. Rep between ** for other side. Continue working short rows until all ten sets have been worked."
The additional fabric created with short rows increases the circumference of the finished sweater front without increasing the cross-sectional width, aka back-width measurement.
An oval is a good approximation to the cross-section of the body at the chest. Without a bust, the front half of the circumference is 18" (46 cm). Push out the bust by a couple inches (5 cm) and the front half is now almost 21" (53 cm).
The formula for calculating the circumference of an oval looks like this (the kind of thing computers are good at):
circumference ≈ π(a + b) x 3 x ((a-b)x(a-b) ÷ ((a+b)x(a+b) x (√(-3 x (((a+b)x(a+b)) ÷ ((a-b)x(a-b))) + 4) + 10)) + 1) where a and b are the two radial axes of the oval
Short-row darts work because the length added effectively creates a fold in an otherwise flat surface, in the same way that inflating a football (or rugby ball) increases the distance from side to side.
Do you need more width across the bust?
In the scenario above, we did not add need any extra stitches for width.
What if, however, your "ride-up" distance does not provide enough extra width? There are two situations where this can happen. Imagine the following scenario. You are making a semi-fitted sweater with a two inch (5 cm) ease allowance at the upper chest, for a finished circumference of 38" (97 cm) -- or 19" (48.5 cm) finished back width. In both cases your "ride-up" distance will be one inch (2.5 cm). Stitch gauge remains the same as before.
Your full-bust measurement is still 41" (104 cm) and your upper-chest measurement is 36" (91.5 cm). Your back-width at the full-chest is almost the same, or less than, your back-width measurement at the full chest. But we know that you need a finished front width of 22" (56 cm) to prevent the fabric from stretching over the bust area:
fullChest - finishedBack = 22 in. or 56cm frontWidth
Subtract the finished front from the long-circumference-calculation ÷ 2 above gives about 1.25" (3.2 cm) extra distance across the front per inch (2.5 cm) of ride-up. The width still needed is found by subtracting the finished back-plus-extra distance from the front width needed:
22 - (19 + 1.25) = 1.75
In this example, at least 1.75" (4.5 cm) of extra width is needed.
Your back-width at the full bust is significantly larger than your back-width at the upper chest. In this case use your full-chest width rather the upper chest as as starting point when determining finished size. You may still need to add a few stitches for extra width in front depending on ease & ride-up, but this will give you a better fit through the back.
How to add Width
There are several ways to add extra width when needed.
When knitting from the bottom, one way is to add them gradually along with your short rows: Use the shadow wrap short-row method and instead of knitting the twin stitches together, knit them separately, which gives 2 increases per short-row.
When knitting from the bottom, use vertical darts (or princess darts).
Add additional stitches across the front either above the bust (top-down knitting) or below the bust (bottom-up knitting). This method works well when working cable or other patterns where the extra stitches need to be worked in carefully. Then decrease the same number after knitting the bust area.
Use Viennese seams (top-down) -- this is an advanced method.
Use the full-chest measurement instead of the upper-chest measurement when determining finished size at chest. This can be a good option for raglans and modified-drop sleeve sweaters.
Would the design work with additional ease? Read more about ease at https://www.blog.knitwiz.com/post/all-about-ease
Wow, that was a lot of information. I hope it's enough information to help you modify your patterns. Another way to go is to create or convert your designs with KnitWiz. Then you won't need to worry about modifications, as your instructions will always be generated to fit. Any questions, you can always reach me at firstname.lastname@example.org.