Crop Top & Tankini

Because You're Going To Ask If I Don't!

The tankini is nothing more than the top half of a one piece. It is usually made with spaghetti straps, but there is no reason why you couldn't have wider shoulder straps or even turn it into a halter or add cups or literally anything you might do with a one piece. The photos below show just a handful of the many variations possible.  In it's most basic form, it is probably the simplest item of swimwear to make but you have to ask if it's worth the effort to make a one piece block if all you want is a basic tankini.


Many will make their own tankini block based on just a bust and length measurement ... I'm not convinced because there are so many bust styles which require starting at the one piece block. I also like tankinis to be properly fitted and darted for the bust ... larger busts really need a shelf bra (or an wire/cup in the lining). There are so many variations that it's really up to you. The demonstration here is to explain the pattern making principles of a basic tankini and leave you to add varying styles from other sections.

Photos found on the Internet (I do not own copyright);
used for the purpose of illustration/education only.

This lesson will create both the tankini and the crop top patterns (you can use the crop top as a shelf bra for the tankini). The tankini dart is curved off and the bust section of the front panel is gathered/eased into the corresponding section on the back panel. I would not gather the tankini without the shelf bra ... instead leave the dart in if you don't want the shelf bra. If you just want the crop top only then skip steps 3 to 8.

Step One

This pattern is based on the Women’s One Piece Block we created previously (using 12% horizontal negative ease and 0% vertical ease). 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.

Trace around your one piece block and draft a guide line for the garment hem about 5cm below the leg line at the side seam (red line). This is an arbitrary line and can be as low or high as you like but should really extend beyond the waist band of whatever bottom style you wish to wear with it. Consider that when you sit down the hem line will rise about 5cm and you still want it to cover the bikini bottom. That said some of my younger students like the hem line at the waist line so it's really up to you.

Draft a guide line 10cm up from the bust point and square across to centre front.

Step Two

Draft in the neckline in the style of your choice. Start about 3-4cm above the bust line at centre front and curve upward to approach the strap point at 45 degrees. Continue down to the side seam making a right angle at the strap point. Your design line should cross the side seam at least 2-3cm above the bust line but can drop below the bust line slightly at centre back. If you want to drop the centre back even further you should make the spaghetti straps cross over at the back. Note you cannot drop the centre back so far if you want a shelf bra!

Step Three

Extend the side seams down to the hem line.

Step Four

You don't have to do this step if you want a really fitted tankini, but I find that if you take some of the waist reduction out of the garment it doesn't tend to rise as much (note all tankinis will rise over time given the chance and there's nothing you can do to stop it definitively). The red line is another arbitrary position but take more shaping out of the front waist than you do from the back waist, making sure that your side seams are of equal length.

I can also hear some of you asking why I went to so much effort to create a block with negative ease and then just eliminate most of it in one swoop. The block serves two purposes; firstly it gives me a sense of proportion, and secondly by basing it on this block I can make sure everything lines up with any style variation I use in the bust section.

Step Five

Draft in your hem line such that it forms right angles with the centre back, side seam and centre front. If you're designing for retail, ensure the hem is the same front to back, if not slightly longer at the back.

Step Six

Smooth a curve gently over the dart and notch the front and back pattern pieces so you know where to ease one panel into the other. If you aren’t going to make a shelf bra then ignore this step and leave the dart. You could lower the dart to a French Dart position if you want or even turn it into a princess line (as seen in one of the photos at the top ... the choice is limited by your imagination.

Step Seven

Remove unnecessary guidelines. If necessary retrace the front and back panels. Add seam allowance to the pattern based on how you intend to assemble it. I've shown this pattern with 10mm allowance for overlocked seams (8mm to blade plus 2mm off cut) and 10mm allowance for folding over 9mm elastic. Do not elasticate the hem line, simply fold over and cover stitch. If you were to use a binder attachment to apply the elastic and casing fabric to the top edge (as I will here), then you wouldn’t need any seam allowance on those particular seams

Finally, be sure to clearly label your pattern pieces with a title, panel name, garment size, cutting instructions, author’s name, date and revision number.

Step Eight - Pregnancy Alteration

I often get asked how to modify the tankini pattern for pregnancy. It's really easy. Simply rotate the section below the front waist about 10 degrees per trimester on average. Do not alter the back panel at all. If you are really enthusiastic, keep your pattern and rotate it back after pregnancy as there is enough fabric in the front panel to convert it back.

Step Nine - Crop Top / Shelf Bra

For the Crop Top/Shelf Bra, go back to Step Three, draft in the empire line (red line) about 8-9cm below the bust point (the underwire is represented to help you picture where it sits), making it intersect the side seam and centre front at right angles. Continue this line on the back panel. If you were making only the crop top you might either narrow the back strap down to put in a bikini clip or widen the back strap for extra support. This should demonstrate why the neckline should not be lowered too far at centre back!

You could also use the crop top as the top half of the tankini, with matching shelf bra underneath ... like an empire line one piece without a bottom.

Step Ten

Remove all the unneeded lines. Draft in a new guide square down from the bust point and rotate the dart closed at the side seam.  If you're only making a crop top you can join the front and back together as I've done below ... or not, up to you. Smooth off the curve at the side seam (red line) if you join them together.

Step Eleven

The top image is now either the wrap around shelf bra of a tankini or a crop top.


If it's going to be a crop top you need to remember it's going to need a bikini clip. So, I've shortened the strap by 2cm to allow for the loss of tension due to narrowing of the strap .... AND I've shortened it a further 2cm because the bikini clip is 4cm wide.


Do NOT shorten any of the strap length if your're making a shelf bra.


The lower image is the crop top ready for a bikini clip. My crop top is bound all the way around so I've only added seam allowance to the dart and 2cm for the fold-over into the clip. 10mm seam allowance has been added to the bottom for a soft elastic to go under the bust and tension the shelf into place. Notice I haven't pulled the dart back for either the shelf bra or crop top ... this is a support garment and it supports better at full length.

Finally, be sure to clearly label your pattern pieces with a title, panel name, garment size, cutting instructions, author’s name, date and revision number.

Follow me on ....

  • Instagram
  • Facebook Page
  • Facebook Group

If you find my website helpful, please consider sharing it with others,
or linking to it from your own page.

The real value of knowledge is in sharing it on!

© 2020 by Pattern School Online