One-Piece Swimsuit to Tankini Tutorial

If you don’t feel like listening to me whine, feel free to skip down to the ******

Before I show you how I did this, can I just say that bathing suit shopping stinks? Especially after kids. Through hard work, I lost all the baby weight (and trust me, I gained more than the recommended amount both times) twice, but my dear Tater and Bean have left other marks on me (and I’m not talking about the ugly c-section scar; don’t talk to me if you’re one of those people who have to look hard to find yours). Marks like extra stomach skin that hangs over anything that touches my waist. Marks like boobs which have mysteriously gotten bigger and smaller at the same time (They’re flatter, but need a bigger cup size – for all the extra skin?) and migrated from their BC (Before Children) positions. So while I used to happily find bikinis at any shop I went into, I now need tummy control, underwire, boning and other torture devices to smush everything back into a semblance of my BC body.

And here’s what I really don’t get – I can find bras and underwear that fit and flatter with no problem. Why is it so hard to make swimsuits that do the same?

********Whew, rant over. Thanks for bearing with me. On to the tutorial.

So, one pieces are tricky, kind of like dresses, because they have to fit right in so many places. I found this really cute one piece (Old Navy)  that did all the right things for my body (things that swimsuits from much more expensive stores were not achieving) except it was saggy in the behind. Which I discovered the first time I wore it to the pool, so too late to return.

The other problem with one pieces is that we’re going on a beach vacation, and I intend to spend all day in my swimsuit, and I would prefer not to have to strip to go potty.

So after weeks of ordering (and returning) other suits, trying on other suits, and a big ol’ debacle of an attempt to make my own, it finally occurred to me to go back to Old Navy and find a coordinating bottom (heck, at this point I was ready to go with basic black on bottom if nothing came up, but I found a zig-zag print that had this color in it) and then turn this top into a tankini.

I have two other tankinis, both from BC, and I couldn’t wear either of them because of that ring of skin between the top of my bikini bottom and the bottom of my tankini. Also, I hate the loose tankinis that just float up when you get in the water, defeating the whole extra coverage thing a tankini wearer is probably going for.

So I cut this swimsuit off right at the top of the legholes, ensuring that it would reach to my bikini bottoms without the skin tire in the middle. The control max lining and my finishing will ensure that it won’t float up. Win/Win for me!

If you look closely on the right and left, you can see how the elastic from part of the leg holes is still attached. To match this (and keep my top down) I cut 3/8 elastic to the same length as the now raw edges, one piece for the front and one for the back.

I used my serger with the knife OFF to sew the elastic to the inside of the raw edges. If you don’t have a serger, zig-zagging works here too.

Now just fold the elastic in, and top stitch on the outside with a double needle. At the edges where there was original elastic, I folded it part way under so it now looks like a continuous seam.

Incidentally, I like these double needles for knits. I order them two at a time in case I break one. I was going to link you to them, but they’re becoming harder to find (I’ve used Amazon sellers). Makes me wonder if I should have ordered more than 2 last time.

And now I have this to wear on vacation

Hooray - you read the whole post! Wanna hang out more? Check out the best sewing pins with me on Pinterest, join our Facebook discussions, get your daily sewing fix and behind the scenes scoops on Instagram, and your weekly updates/free pattern access through the newsletter


  1. says

    TOTALLY – If underwear people can get it right, why can’t bathing suit designers? It’s almost like they are TRYING to mock us.
    Which is why I this post is very timely for me. I bought a very cute one piece a couple of months ago. It has a front panel of ruching over the suit. However, when I got into to the pool, the whole thing stretched out making me look like the saggy-baggy elephant.
    I am going to attempt to take it in, but I am scared to death. I guess I don’t have much to lose. But, I don’t have a serger either. So, wish me luck!

  2. Jessica says

    I actually appreciated your ranting. My first baby left awful marks on my body and here I am pregnant again watching helplessly as my body disfigures even more. Ah the price of mommyhood. I’m sorry for your changes, but honestly it’s nice to know there are others out there like me! Great job on your swimsuit. I ended up finding a tankini that looks like a swim dress so lots of coverage and I’m excited for that!

  3. LisaRae says

    Your rant is so similar to mine, I gained far more than I needed to with my first, and was as careful as I could be during my second pregnancy, but at the end of the day I’m still sitting at a 50-60 pound weight gain that I have had to lose. I will say that the weight gain was well worth the joy that came afterwards though.

    Also, I found my perfect bathing suit at old navy as well, they have great suits this year!

  4. says

    I completely identify with this! I have it all too after my two kids — C-section scar, extra skin, flabby abs, and stretch marks to boot. I won’t even consider a bikini anymore. We’re doing a beac vaca this summer also so I’ve started the discouraging process of swimsuit shopping. Nothing better to bring down an exhausted mother of two! Might have to try this with one or two of my old stretched out one pieces though. Great idea!

  5. Sherri says

    If it makes you feel any better… I’m only 24, no babies, and I can’t buy a bra for the life of me. I’d be a 30C or a 32B, (because I need the underwire that big) but I fill maybe half the cup on a good day.
    I’d love a one piece swimsuit but I’ve never tried one on that was even acceptable.

  6. says

    Your post has struck a cord with most moms. I am on the same page as you. After my 3 kids I have excepted things will never be the same. Thanks for your wonderful Idea. I will be redoing my suit too.
    Rose @ {A Rosie Sweet Home}

  7. Ann @ makethebestofthings says

    What an excellent idea and well done! This could make any number of cute and cool summer tops to wear with shorts, since I don’t do bikini bottoms, lol! Gonna try this and soon.

Share Your Thoughts:

Your email address will not be published. Required fields are marked *