Summer knitting in the Fall: A tutorial for a Mitered Square Summer cotton tank top

I love all things Autumn: rain, watching NFL, Thanksgiving, winter squashes, knitting by the fireplace with a hot drink. So I decided to knit a cotton summer top. Because I make sense.

knitting mitered square tank top

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How to…

This is more of a tutorial than a pattern. I’ll give instructions on how I created it, but feel free to make any and all modifications.

The schematic shows how the tank is constructed. (And please feel free to admire my amazing MS Paint skills.) Note that the triangles labeled A and C on the sides are actually full squares that wrap around to the other side. Squares labeled A are worked first, separately. B squares are worked next by picking up stitches from the A squares to connect them together. C squares are worked after that by picking up stitches from the B squares. Triangles labeled D and E are completed next. Finally two full squares with straps (F) are added.

knitting mitered square tank top schematic

  • Cotton or bamboo or linen yarn in a Dk or sport weight. The sample was made with Bamboo Pop by Universal Yarn, which is a DK weight of 50% cotton and 50% bamboo. I used approximately 550 yards, but didn’t keep track of how much of that was main color vs. contrasting color. I suggest knitting a square, calculating the yardage of that one square, and multiplying it by the number of squares you’re going to make. (17-ish if you’re following the schematic). Add some for the straps and edging, and you can get a decent approximate yardage needed.
  • Needles, size appropriate for yarn used, or maybe slightly larger for a nice drape. I used a size 5 for the main parts, and a size 4 for the edgings.
  • Tapestry needle for weaving ends.
  • K – Knit
  • P – Purl
  • St(s) – Stitches
  • CDD – Center Double Decrease
  • Sl  wyif- Slip with yarn in front
  • RS – Right side
  • WS – Wrong side
  • SSP – Slip, slip, purl

Before starting, let’s figure out sizing and some math. For sizing, measure around the bust and decide on ease. I recommend zero ease or even a slight negative one, because I tried a couple of inches of positive ease at first, and it could have fit a couple of elephants instead of my young daughter. So, the circumference will be bust size in inches plus whatever ease (or not) you want to add (or subtract). Once you know the circumference of the top, divide it by 4. That will be the length of x in the square picture. Also, knit a swatch and calculate gauge (sts/inch).

knitting mitered square tank top schematic

The chest circumference for the sample was 27 inches, so each x equals 27/4 or 6.75 inches.

Because you know the length of x, you can calculate the length of “a” using the Pythagorean theorem since the square forms right angles (more or less). This will be the length of one side.

knitting mitered square tank top equation

Because the sample had an x length of 6.75 inches, the length of “a” equals 4.77 inches.

Now that you know the length of one side, you can calculate how many stitches are cast on for one side using your gauge:

a * (sts/in) = stitches per side.

My gauge was 5.5 stitches per inch, so I needed to cast on 26 stiches for each side of a square.

Let’s set stitches per side equal to z. (So, my z = 26 stitches.)

Row A Squares

These are the only squares that will be worked separately. Cast on (2z) +1 sts. (For my sample, I cast on a total of 53 sts, 26 for each side, plus the center stitch.) Turn.

Setup: Knit z sts, sl1 wyif, K to last st, P1.

Row 1 (RS): Slip1 knitwise, knit to middle 3 sts, CDD (Slip 2 sts together knitwise, K1, Pass slipped sts over.) K to last stitch, P1.

Row 2(WS): Sl1 knitwise, K to center st, Sl1 wyif, K to last st, P.

Knit these two rows for awhile until you decide you want to add a new color. On a right side row, work with the current color until you get to the last st, then purl that with your new color. Continue Rows 1 and 2 with new color until you feel like switching it back. I highly recommend attaching/weaving in color changes while you’re knitting to avoid weaving in a bazillion ends later.

When you have 5 sts left after working a WS row, on the RS, Sl1 knitwise, CCD, P1. (3 sts remain). WS: Sl1 knitwise, Sl1 wyif, P1. RS: CCD. Cut yarn leaving a long tail, and pull through from the back to the front of the st. This st will be used later, so just leave the tail through it for now to prevent unraveling.

Work 3 more squares the same way.

Row B Squares

The second row of squares will connect the first squares together.

With RS of a Row 1 Square facing you and starting at top, pick up z sts in slipped sts along top left edge. (Do NOT use the live st at the very top of the square.) Pick up a st in one strand of knot at bottom of square and one strand of knot in another Row 1 Square. This is kind of awkward, but I found using a crochet hook made it a bit easier. Now, pick up z sts along the slipped sts on the right side of the other Row 1 Square. Again, do NOT use the live st at the top of the square.

knitting mitered square tank top

Setup (WS): Knit to center st, Sl1 wyif, K to last st, P1.

Work Rows 1 and 2 from Row A Squares, changing colors as desired. Complete 3 more squares in a similar way connecting all the Row 1 Squares. (Tank will not be flat anymore after all Row A squares are connected to Row B squares.)

Row C Squares

Row C Squares are worked very similarly to Row B Squares. Pick up sts the same way (leaving the top live sts of B squares alone for now) with the following exception: When you get to the bottom corner of the square, pick up that live st from the top of the Row A Square and place it on your right needle. Pull the tail end out of the st to weave it in later. Do this for all 4 Row C Squares.

Knitting the Bottom Partial Squares (D)

Turn  work upside down. You will be picking up sts from the cast-on edge of the Row A Squares to fill in those triangles, using the following method:

On left edge of upside-down square, pick up z sts, pick up 1 st from bottom center st of Row B Square, then pick up z sts from right side of next Row A Square. Turn.

Setup (WS): K to center st, Sl1 wyif, K to last 2 sts, SSP. (Slip slip purl: slip 2 sts knitwise separately, pass them back to left needle. Purl together through the back loop.)

Row 1(RS): Sl1 knitwise, K to center 3 sts, CCD, K to last 2 sts, SSP.

Row 2 (WS): Sl1 knitwise, K to center st, Sl1 wyif, K to last 2 sts, SSP.

Change colors (or not) as you did with previous squares.

Work rows 1 and 2 until you have a single stitch left, the cut and weave in. (I ended up with 4 sts, so I did a CDD, except I K2tog before passing my slipped sts over.)

Knitting the Back Triangles (E)

The two triangles at the back top are worked by picking up stitches along the slipped edges of the Row 3 Squares (including the live st at the top of the Row B Squares). You can also include the live stitches at the top of the C Squares in your picked up stitches. Decreases are done the same way as the bottom triangles. Work this way (including color changes) until you have desired number of live sts left for the strap, ending with a RS row. (My strap was 13 sts wide, not including edging.) Cut a long tail, and place live sts on a holder.

knitting mitered square tank top equation

Front top Squares and Straps (F)

Pick up sts along the edges along Row C Squares as previous (again, including the live stitches at the tops of Row C Squares if available) and work until you have the same number of live sts left that you have on the back triangles. Now, continue to work back and forth on the straps without decreasing, but slipping the center st on each WS row. Work straps until desired length, ending with a WS row. Place all live sts on needles and Garter Kichener stitch the live sts on the strap to the live sts on the back triangles. (Here is a video on grafting garter stitch.)


For the edging, pick up sts in the slipped sts at bottom, armholes and neckline. Work garter st (or other desired edging) around. You can add some short rows to raise the neckline or armholes if desired. For the sample, I added a few sets at the front of the neckline using simple wrap and turns. Bind off loosely and weave in ends. Block as desired.

Please contact me with any questions!

Happy Thanksgiving!

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