Knitting sweaters that truly fit is an art—and nowhere is that more apparent than when shaping for the bustline. Bust darts can transform your handknits from “good enough” to “just right,” offering extra length and shaping where you need it most. But the truth is, not every sweater needs bust darts, and the decision depends on your measurements, your garment style, and the amount of ease indicated by your pattern.
To make this big topic easier, let’s start with the essentials before diving into the details.
Quick Guide to Bust Darts
- What: Two common types—horizontal darts (angled short rows) and vertical darts (princess seams or Viennese shaping). Horizontal darts are most common.
- When: Add horizontal darts if the sweater rides up in front. Vertical darts are useful when extra width is needed, or to draw the sweater in at the waist.
- Where: Darts are placed on each side of the front. Horizontal darts angle down from just outside the bust apex; vertical darts start at or above the waist.
- How: Horizontal darts use short rows for extra length. Vertical darts are shaped by increasing stitches gradually.
- Why: Short rows increase the front length without stretching or distorting the fabric, creating a smoother fit over the bust.
When Do You Need Bust Darts?
Most patterns base the finished chest measurement on the full bust. For some of us though, this is not the best way to determine your pattern size. Often it's best to determine your pattern size based on your upper chest measurement, and then adjust the pattern at the bust area if necessary. In this post we'll focus on adding horizontal bust darts using short rows, which will add both length and width to the front of your sweater.
To determine whether you should add darts, take two measurements:
- Full bust (around the fullest part).
- Upper chest (just under the arms).
If the difference is more than 2" (5 cm), darts can make a world of difference.
Sleeve Styles and Their Role
The type of shoulder construction impacts whether darts are necessary:
- Dropped Shoulder Construction: Boxy by nature and designed with generous ease (often 7–8" or more). Because they drape loosely, and tend to curve downwards at the sides anyway, darts are optional. Note -- For dropped shoulderconstruction, always use your full-chest measurement to determine pattern size.
- Set In Sleeves: Closely follow the body’s contours at the arm opening. Use your upper-chest measurement to determine pattern size. Horizontal bust darts are highly recommended for larger bra cup sizes (C and higher); without them, the sweater may ride up in front. The extra length provided by darts is exactly what prevents this.
- Modified Drop Sleeves: Somewhere in between. Depending on the amount of positive ease, darts may be helpful to avoid ride-up.
How Much Extra Length?
The general rule:
Dart Length ≈ Full bust – Upper chest – 2"/5cm.
For greater precision, measure your ride-up distance:
- Shoulder to waist over the bust.
- Shoulder to waist down the back.
The difference between these two measurements will tell you how much extra length your sweater needs to fit properly in front. In the example below, the difference between the shoulder-to-waist measurements is three inches. Therefore, a three inch dart is required.
Where to Place Bust Darts
Typically, the fullest point of the bust is anywhere from one to three inches (2.5 - 7.5 cm) below the underarm. Whether knitting top-down or bottom up, you'll need to know the vertical drop from your shoulder bone to the fullest part of your bust. It's best to take this measurement while wearing a bra and looking in the mirror. Then note where this measurement falls on your pattern.
For example, if the underarm depth on the pattern schematic is 8", and your shoulder-bust measurement is 9", your fullest bust measurement is 1" below the underarm shaping.
Knitting Top Down?
Begin short-row shaping at the fullest point of your bust; in the example this is one inch after casting on at the underarm. When knitting top down, wraps begin closer to the center, and are progressively worked further apart.
Knitting Bottom Up?
In this case, you will be finishing the short row shaping at the fullest point. Since this point falls 1" below the underarm bind off in our example, you'll begin short rows 4" before binding off. When knitting bottom-up, you'll begin short-rows one inch from the side, and wraps are worked closer together as the work travels upwards.
The blue area in the sketch below represents extra fabric added by short rows.
Performing the Calculations
Unless you are using software to get personalized instructions, there's no getting away from math. To determine the number of rows needed, multiple the ride-up length (3"/8cm in our example) by the row gauge. Let's say our gauge is 28 rows = 4"/10cm. Then we'd need work short rows over 28 ÷ 4 * 3 = 21 rows. Round this number down to the closest even number, and divide by 2 to get the number of short row sets needed. In our example we need (21 - 1) ÷ 2 = 10 short row sets.
Before we can calculate the short-row wraps, we'll need a few more numbers:
- The Full-Bust-Width: the distance between breasts at the fullest point (usually, but not always, the distance between the nipples). For our example we'll use a full-bust-width measurement of 7"/20cm.
- The front sweater width: For a size Md in our example this is 21".
- The stitch gauge: 20 sts = 4"/10cm
Since we want the point of the darts at the bust to be at least one inch from the fullest point, add 2"/5cm to the full-bust-width: 7" + 2" = 9". And since our dart should not extend all the way to the side edges, we'll subtract one inch from each side of the front-sweater width: 21" - 2" = 19". So for each side dart we'll have (19" - 9") ÷ 2 = 5" available for wraps. Multiply this number by the stitch gauge to determine your number of stitches: 5" x 5 sts per inch = 25 sts. For each set of short rows we will use 2 stitches: 25 sts ÷ 10 sets = 2 sts per set.
Knitting Bottom Up?
The final instructions would read something like this for a pullover:
Row 1 (RS): Knit across to last 6 sts (before side marker), wrap & turn (w&t).
Row 2 (WS): Purl to last 6 sts (before side marker), wrap and turn.
Row 3: Knit across front to 3 stitches before previous wrap, wrap and turn.
Row 4: Purl across front to 3 stitches before previous wrap, wrap and turn.
Rep rows 3 and 4 eight more times.
Next row: Knit across, picking up wrapped sts as you come to them.
Next row: Purl across, picking up wrapped sts as you come to them.
Knitting Top Down?
The final instructions would read something like this for a pullover:
Row 1 (RS): Knit across to last 30 sts (before side marker), wrap & turn (w&t). Note - 5" dart + 1" at side) * 5 sts/inch = 30 sts
Row 2 (WS): Purl across to last 30 sts (before side marker), w & t.
Row 3: Knit across to wrap, pick up and knit wrap along with its partner, knit 1, w & t.
Row 4: Purl across to wrap, pick up and purl wrap along with its partner, purl 1, w & t.
Rep rows 3 and 4 eight more times.
Why This Works
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.
This is why, most of the time, it's not necessary to add extra stitches at the bust. In case you should ever need it, the formula for the circumference of an oval is:
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.
Or simply try on your sweater to see how it fits around!
Final Thoughts
Bust darts are one of the quiet secrets of a polished handknit. They let sweaters follow your shape gracefully—without pulling or riding up. Whether you choose to embrace short rows, vertical shaping, or simply knit with extra ease, knowing when and how to use darts gives you freedom in your knitting.
And remember: at the end of the day, sweaters are meant to be a joy to wear, and also fun to make Fit is important, but so is comfort in knitting. When you're ready to take on the challenge of bust darts (if you even need them), this blog post will be here for you.
And as always, you can reach out to me at hello@sweetmeadowknits.com with any questions.
Warmly,
