Asymmetric Tanksuit with Waist Cut Out

Asymmetric One Piece Swimsuit Analysis

This is an asymmetric one piece swimsuit suggested for analysis by Georgia (white, no cut-out). The first two photos are by Myraswim (, the second two are mine, the rest are unknown sorry. By asymmetric we mean its not the same from left to right ... typically that means there's a shoulder missing but it can also mean single-sided cut-outs, single-sided ties, single-sided features or all of the above. So I've included a few of those in the slide show below. The last image, although it looks complicated, is no different to all the others except that one part of the garment has been replaced by beads ... this should demonstrate that you can create some really unusual shapes from some very simple foundations.

NOTE: Part of what we all did at Fashion School was look at other people’s high fashion garments and see if we could work out how they were made. This was particularly the case for 3rd year pattern making. The teacher would show us a photo of something from fashion week and give us an hour to make a pattern for it … I loved those challenges. At the end of the hour, the teacher would demonstrate how she thought it should be done and why. Some people out there call this copying or “knocking off” someone else’s design … that’s not what we’re doing here … this is about learning how to make patterns by following a procedure … it’s what we all did and how we learned. I’m not telling you to take these instructions and go manufacture this garment for sale …that is wrong and illegal ... I’m using this design as an example to teach students how to manipulate a block into a pattern that resembles this style (albeit, probably not exactly).

This time instead of demonstrating on the Size 10B/C Women’s One Piece Block we drafted previously, I’m going to base this pattern on the RTW Women’s One Piece 12% Block Set for a Bust size of 88cm, Waist of 68cm and Hips of 93cm. I want to do this to show that the block we start with isn’t important for this type of lesson. Before you start each step, take a good look at the illustration to help you follow the drafting process. At the end of each step your draft should match the illustration.

Step One

Given all the options above we're going to do a pattern for an asymmetric one piece with a shoulder similar to the Myraswim garment, but with a larger cut-out so we can demonstrate both features at the same time. Now because the garment is asymmetric we need both sides of the block displayed at the same time. Firstly I've highlighted the BP top shoulder line in red ... this is the center of our front shoulder strap.

I've also marked two horizontal guide lines in green each 7cm above and below the bust line. This is a reasonably conservative spacing either side of the bustline, of course you can make yours higher or lower for your design, just remember that the stability of this section depends on coverage ... the less you have the less stable the garment, the more tension you'll require and the more ripples you'll get. If you're doing a cut out then try to keep the spacing even either side of the bust line.

I've drawn a blue rectangle from BP to where the waist intersects the side seam, and then divided it vertically in half. By now you should have noticed my like for finding the center of things ... there's a good reason for that ... spandex is softest midway between seams, elastic edges, the line of highest tension, etc.  I like a revealing cut out so our depth needs to fall somewhere between that vertical center line and the vertical below the BP. More on this later. Copy this guide to the back block in the same position.

I've also broken the distance between waist and crotch seam into eighths ... the belly button centers close to the first eighth from the waist so this is a good guage for deciding the lower edge of your cut-out.

Lastly I've placed a bikini clip at the CB bustline. A few people have recently commented that they can't find clips the same size as mine and seem unable to adjust for a different sized clip so I'm now just going to draw my clip in its exact size and not say what that is ... you can draw your clip in your size in the same way and just copy the steps.

Step Two

Next we need to look at how wide our straps are going to be. I've chosen 4cm because I think it'll look better with the other features on the garment and I can carry that same measurement to those locations. So I've placed a 4cm wide rectangle over the guidelines to the shoulders both front and back, and only shortened them by 1cm because they're relatively wide.

I've also placed another 4cm rectangle (carrying the same width) on the front leg line where it's perpendicular to the side seam, and copied it to the same position on the back panel. This gives me a guide for the edge of the cut out so it looks consistent with the shoulder strap. This is arbitrary, but I like consistency.

Lastly I've placed a couple of 4cm high rectangles either side of the bust dart at the side seam for the same reason. These I've then carried to the back panel. They are simply guides and will move later.

Step Three

Now comes the fun part .... we start on the back panel. Draw in the back left bra panel by simply joining the dots at the corners of each guide and the clip. Next draw in the strap line from the top of the shoulder strap to the bikini clip ... there's not too much room for design freedom here. Next draw in a curve from the bottom of the clip, to the center guide line on the waist, to the side seam at the top of the bikini bottom strap.

Step Four

Copy the back bra panel twice and place it at on the corresponding positions on the front panel both at the armhole and at the bottom of the dart using the rectangles as guides ... this is hard to explain so see the illustration. Now you can create a smooth curve from the bikini clip top point, to the neck side of the top of the shoulder strap, shaping it to follow the strap, the top bra guide and the back bra panel.

Next, draw another curve from the bottom of the bikini clip, to the center front of the bottom bra guide, to the center vertical line on the waist, to the top of the bikini band on the side seam .... you can also transfer a copy of the back bikini across to make sure your curve is smooth. See the illustration to understand better.

Lastly draw in the armhole on the front panel from the top of the strap to a point on the side seam that matches the same height of your new curve on the opposite side seam.

Step Five

Transfer the new back bra curves to the back panel again.


Copy the front arm hole curve and place it in the correct position on the back panel to use as a guide to create the back arm hole.

Step Six

Move the point of the darts about 1.5cm away from the bust point. Now some people would rather just gather up this dart and ease it into the side seam and that's fine. I prefer darts as I don't like ripples on a garment and darts are more stable in a narrow section such as this, but it is your choice.

Step Seven

This step isn't essential but I prefer to do it because it makes sewing easier and removes the little 45 degree ripples you can sometimes get in this location. Place a copy of the back bikini bottom section over the front bikini bottom section and wiggle it around a little until it looks a little more natural. Re-curve both front and back smoothly. You may find you need to move the side seam a little more forward to make it look right ... this really reflects the natural position of the leg hole apex on my blocks.

Step Eight

Transfer the new curves to the back bikini bottom section and smooth everything off. If you're thinking creatively, yes you could make this into a tie side too!

Step Nine

Remove all unnecessary lines and add seam allowance. I've added 10mm for fold over elastic and for stitched seams (cutting off excess with the serger). I've added 15mm seam allowance for the clip fold over. Be sure to add a label for style, panel name, how to cut, size information, date/revision and author. Mark any guides with the relevant label.

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