Bust Dart Math!

I guarantee that explaining this will take far longer than it will take you to actually DO the math. Plus, if I were sitting right next to you, I could show you in a nanosecond. But, we have our friend the written word to help us, so here we go: Bust Dart Math!

For a top-down in-the-round sweater, vertical bust darts are lines of decreases that take the full-bust measurement of fabric at your bust and decrease it in size until it matches the measurement under your bust. Thus, we start off with:

1. How much do you need to vertically decrease?

You'll need two measurements of your own beautiful self:
Full Bust (FB): Around your bust at its fullest part.
Under Bust (UB): Around your ribcage, just under your bust.

Now, subtract:
FB minus UB equals Total Decrease Amount (TDA).

However, we need to convert that TDA measurement to rows/rounds and stitches so we know what to knit, right?

2. How much are we decreasing in each individual dart/decrease round? And then, how many decrease rounds do we work overall?

  • Figure out the stitches-per-inch gauge.
  • Divide that gauge into four (4 divided by gauge) because we are working four decreases for each round (two bust darts each side; each dart is a line of vertical decrease stitches). The result is the Decrease Amount Per Round (DAR).
  • To find the number of decrease rounds: TDA divided by DAR = Total Decrease Rounds (TDR). (Hold onto that TDR number for a bit.)

3. Where do you put the dart (decrease) stitches in each round?

Remember that we are assuming a top-down sweater worked in the round. Here's how we figure out precisely where to put the dart stitches in each round:

  • Make sure you have marked the midpoint of each armhole on your partial sweater. This marker is at the "side seam," so to speak. We'll do all the counting/measuring in relationship to that marker, so it's pretty important.
  • Find this "side seam" location on yourself, too. (Go ahead, cheat: Put on a thin shirt that actually has side seams.) Measure forward from the side seam to your nipple. This measurement, side seam to nipple, we'll call N.
  • Try on your partially-knitted sweater, and place a safety pin (carefully…) next to the stitch closest to your nipple (by "next to," I mean on the "armhole" side of that stitch). Count the stitches from this marker to the side seam marker and you have what we'll call Total Side Stitches (TSS). (If all the math works out perfectly, then your stitches per inch gauge times your TSS should equal N, but don't stress too much about this one, because your bust may be stretching the gauge out a bit!) NOTE: Use a safety pin or a marker that looks very different from your other markers to mark the nipple stitch, because you will want to remove this one before knitting and you won't want to get confused which marker is which.

Location of the Center Dart: (On Bertha in the photo above, this dart is represented by the BLACK clip.) This dart is easy. You want it to be about .25" away from your nipple, towards the side seam. Figure out how many stitches that is (use your stitch gauge or just measure), and place another marker at that spot. Whoo! Center Dart Alert! (Now do the same thing on your other side for the other Center Dart.)

Location of the Side Dart: (On Bertha, this dart is represented by the PINK clip.) This one is a leetle more tricky, but we can handle it. There are two ways to figure out this dart: using measurements, or using actual stitch counts.

Measurement Way: N minus .25" was where we put the Center Dart, right? Well, the Side Dart is placed at the point one-third of the remaining distance from Center Dart to side seam: [N-.25] divided by three equals the distance from Center Dart to Side Dart, measuring from nipple towards the side seam. Place a marker there for the Side Dart; do this step again for your other side. (See how on Bertha the pink clip is about a third of the way between her non-existent nipple and her "side-seam"? That's what I'm talking about here.)

Stitch Count Way: For this, you have to figure out how many stitches are in the .25" you used for the Center Dart above. Got that? OK, then: [TSS minus that number] divided by three equals the number of stitches between the Center Dart and the Side Dart. Place marker and repeat on other side.

(Note: On Bertha, her pink clip is a little bit further forward than the "one-third" rule. That's because Bertha's curves are about a B or C cup; my "one-third" rule/suggestion/guideline/loosely-discussed-between-friends-number is what I used for my D/DD cups. If you did the exercise with the hair clips and the loose tee shirt, you may have your own customized measurements for the placement of the Center Darts and Side Darts. Use those. They're all about you, baby!)

4. Now, the knitting instructions:

  1. Remove the safety pin that marked the location of your nipple. (If you leave it in, you might get confused which marker is a dart and which is your nipple. Amusing, but not very helpful.)
  2. Starting at the first "side seam" marker, work to three stitches before the first Side Dart marker, ssk, k1, slip m.
  3. Work to three stitches before the first Center Dart marker, ssk, k1, slip m.
  4. Work across the center front of your sweater until you get to the other Center Dart marker, slip m, k1, k2tog.
  5. Work to the other Side Dart marker, slip m, k1, k2tog.
  6. Finish this round, and then work one round even.
  7. Repeat those two rounds (one dartly decrease round and one work even round) a total of TDR times (the number you held onto in Step 1).


Wow. Know what? YOU HAVE DARTAGE!! Notice that the decreases will form vertical, diagonal lines that are actually quite attractive.

An example is always better, but we've run out of space to do that today. We can do that on Friday, plus I can start answering questions then, too.


P.S. Have something to add to the discussion? Need to ask a question? Leave a comment! I'm not quite actually and fully back yet due to Unforseen Circumstances, but remote access is a beautiful thing.

Previous Bust Dart Posts:

The Return of The Bust Darts

Introduction to Darts: Vertical and Short-Row

Bust Dart Placement

Getting Started With Your Bust Darts: Shoulders To Bust

Other Things You May Like to Check Out:


Knitting Daily Blog

31 thoughts on “Bust Dart Math!

  1. OH MY GOSH—-this is way over my head. I hope some of you understand this, I sure don’t. I don’t think that I will do darts unless by some micracle I will understand it.
    You are a genius, Sandy, I am not.

  2. I’ve only read this hurriedly, hardly ever having needed bust darts for reasons you’ll see if you read on.

    I’m blessed my well endowed friends tell me with small breasts. I think early on in this series you mentioned that for people like me, one instead of 2 darts would suffice, and I agree. So wouldn’t I divide the gauge into 2, not 4 to get my DAR?

  3. I have loved this series on bust darts and the previous ones on sweater shaping. As a fairly new knitter, I have really learned from them. Thanks for such clear help on these topics!

  4. OK – this is really great & as an E+ girl I really appreciate it! ….but honestly, I much more often knit bottom up – how can we interpret this information in the other direction? WIll you be giving us information for Bust Darts Bottom Up???

  5. Math is just numbers, it can not hurt you…much! I do hope all is well with you Sandi and all that is holding up your return is a delayed flight!

  6. Thanks for all that info Sandi. I did find step No 2 confusing, even though I am a maths teacher. Here’s another way to do Step 2. Mathematically it is the same, but logically a bit different, so it may help some others.

    2. How much are we decreasing in each individual dart/decrease round? And then, how many decrease rounds do we work overall?

    * Figure out the stitches-per-inch gauge.
    * Multiply this stitches-per-inch gauge by the TDA you found in the previous step. This will give you the total number of stitches that need to be decreased. (TDS)
    * To find the number of decrease rounds: TDS divided by4 (because we are working four decreases for each round, two bust darts each side; each dart is a line of vertical decrease stitches) =Total Decrease Rounds (TDR). (Hold onto that TDR number for a bit.)

  7. I agree with Hannah: well-endowed women need darts for bottom-up knitting. Top-down projects usually have raglan seams, which are VERY unflattering to us, because they lead the eye down an ever-widening line. (But it’s not that hard to reverse the math, so, thanks for the tutorial.)

    Question: do these darts replace short-rowing at the bust (horizontal darts)? Would you ever use both in one sweater?

  8. I’m sure this is much easier to do, rather than to read about. You are brilliant for coming up with all of this math, though. Whoever your algebra teacher was should be very proud.

  9. I have to say that the instructions for the darts make me giggle. As an older once-well-endowed lady, i now find that actually finding a “consistent” place where my nipples may be located is some what of a challenge these days!! Depending on the undergarments and any number of other factors, they can be a bit north, a bit south, off to one side -anything but symmetrical!! my hat is off to you younger gals, good luck with the math but for myself, i think i will stick to cardigan sweaters!!

  10. I agree with TheresaT that we busty folks are better off with bottom-up knitting. I think I understand how to convert these center darts, but if you can tell us, that would be helpful. And I also wonder how these darts interact with horizontal darts, if at all.

    I love the idea of having 2 kinds of darts because pattern stitches and color work often require adaptation.

    Great series. Thank you.

  11. Fabulous as usual Sandi!

    I think we’ll all be amused at this point by CastOn’s Knitting Scout Badges for Math (about half-way down this page: http://www.cast-on.com/?page_id=123 )

    Very funny, and so true. Thanks Sandi–I can’t wait to try one of the Knit so Fine sweaters, which I think would really lend itself to this technique.

  12. Sandi!
    Thanks again for a wonderfully helpful post! These were right on time – I just started knitting my Hot Tomato a few days ago.
    I have a few questions, though:

    1. For a B size girl as myself, you wrote (a year ago on the first Hot Tomato posts) that one dart per side was enough. Where do I place that one dart? Should it be somewhere in the middle of the two darts, or some other place? Or shoud I just have two shorter darts?

    2. When I decrease stitches from the front of my sweater, shouldn’t this be taken in concern when i continue knitting the torso part? What I mean is, I now have less stitches than the pattern calls for, and they are all reduced from the front, which leads to an unballanced sweater – back is wider than the front. How do I deal with this?

    Thanks, Galia

  13. Hello Sandi,

    Oh well, I thought it would be really complicated but right now (after a good night’s sleep and a big cup of coffee) it seems pretty straightforward.

    I was wondering, would bust darts make small “assets” seem bigger? I don’t have much to show off, plus I am tall, a bit overweight and have really broad shoulders for a woman. This adds up to me only wearing “wonder bra” to be able to show a little bit. And still, I look pretty flat chested.

    Not to mention that I always have to alter patterns to make them fit my broad shoulders.

    Thinking about this, this seems to be a good thing to post in the forum.

    Cheers, Julia

  14. Sandi,
    Under Step 4, #7, should the instr. be to refer to a total of TDR times (the number you held onto in Step 2) instead of (the number you held onto in Step 1)? because you say in Step 2 under 3rd bullet that we should hold onto that TDR number for a bit? Could just be a typo.

  15. This has all been very entertaining and enlightening, but what about us less endowed girls? I am an A cup – on a good day. I would like flattering (not flattening) styles, too. Store bought clothes always seem to have extra material on top, and therefore accentuate the negative, if you know what I mean. Will darts help us, too? Or should I just knit to the underbust measurement and hope the little girls will poke out attractively?

  16. hi – this is actually a request – i couldn’t find another place to leave it so i hope you don’t mind my leaving it here. i’m interested in the aran felted hot water bottle pattern from interweave, summer 2002, but i think this is a sold-out issue (at least i can’t find it for sale anywhere). would you consider posting this pattern for sale in your online store?

    many thanks for considering this.


  17. OK, I am back calculating this right now since I am doing a bottom-up cardigan and I want to add bust darts. My thought was that you can measure N and divide by stitch gauge and get what you WANT your TSS to be. You the use the TDR math to add to it. As to placing the pins< I plan to do it where the clips were placed on bertha to start the darts. My cardi back is done so I was planning to pin and try on as I go. Anyone has any thoughts on this I would be grateful. Or maybe Sandi our Dart Guru could do another post... (hint hint)

  18. A great big thanks to Sandi for posting the calculations on bust dart math-I greatly appreciate it. I would also like to join in the request made by others to have the calculations posted for sweaters worked from the bottom up. I have a basic question about the use of bust (or any) darts. If one is working an intricate pattern, e.g., stranded color work, aran/cables, or a complex lace pattern in the bust area (or anywhere else one places the darts) wouldn’t this be a problem since the whole pattern will be thrown off by the decreases in the dart placement area? In other words, wouldn’t dart placement only work in solid color, stockinette (or other simple stitch) patterns? Thanks in advance for all your help!

  19. The first line of the Knitting Insturctions did not print out
    completely. The sentence is cut in half horizontally.
    Could someone please tell me what it says? thanks. Gloria

  20. I really like the worksheet — nice clear way to lay it out. But I can’t seem to find what G represents. Can anyone give me a hint? Thanks!


  21. Never mind. When I opened up the worksheet after downloading it, I see it: F times C or total stitches to decrease. I need to go back a couple messages to understand how to position the first decrease row working from top to bottom, but I think I understand. Pretty neat! Thanks –

  22. You are so awesome! Working bust darts actually seems doable to me now.

    You are constantly challenging me to become a better, more fearless knitter, and it’s working! Thank you, thank you, thank you!

  23. Gloria, the first line of knitting instructions goes like this:
    Starting at the side seam marker, work to 3 sts. before the next side dart rn, ssk, k1, sl m.
    Hope that this will help you.

  24. Sandi,
    Thanks for the instructions for the bust darts. My problem now is not being able to download the Excel worksheet that does the calculations for me. I am using Vista Premium on my computer, and every time I have clicked on the download line my computer goes into a fit of rapid flashing as it is trying to open the new page, but can’t. Since it is flashing so quickly, I can’t close the window and have to shut down the computer and reboot. I need help desperately and am open to any suggestions.
    Charlotte Unversaw in Indy

  25. I understand your formulas, so maybe I don’t need the Excell worksheet. However, when I try to open it, I can’t see the worksheet, only the name of an empty file. My computer doesn’t do what Charlotte’s (also in Indy) does. Unlike when I open patterns, this never goes to the spreadsheet. I am not usually a computer idiot, but what should I do?
    Roberta who is also confused in Indy

  26. Sandi;

    Thank you so much for breaking down bust darts! I find this MUCH easier to understand than doing short rows, AND you even created an Excel spreadsheet…Awesome! I’m looking forward to implementing this in my next knitting project…if I could only decide what to knit next….

    Lindsay in Grand Rapids

  27. I guess the Excel worksheet would be great–if I could open it in plain old Excel and not have to purchase new software first. Help! Why doesn’t the worksheet simply open for me?

  28. I’m still working in old Excel 97, and was afraid this document wouldn’t work for me, but lucky me! It not only works, it is super! I saved the worksheet to my documents, then made a quick change to the Knitting Instructions I cut the instruction “Repeat these two rounds H times.” and copied it into the cell below and then replaced it with this formula =”Repeat these two rounds ” &B24&” times.” That way, when I print this out for each pattern, the number is already there and I don’t have to handwrite it in. I also added a rounding formula to G and H, since I can’t a fraction of stitch or repeat a row a fraction of a time, “=ROUND(SUM(B20*B11),0.1)” and “=ROUNDUP(SUM(B22/B13),0.1)” respectively. I’m just a bit lazy and don’t want to have to think each time I want to use the instructions!