How to Make a One-Piece Long Sleeve Swimsuit: Pattern Hack Tutorial

By Lindsey EssaryJun 11, 2025

Supplies Needed

Swim fabric
Swim lining (Note: For this particular suit, use a thinner lining rather than swim fabric for the lining, as some seams become bulky and two layers of swim fabric would be too thick)
Swim elastic
South Shore Romper pattern (you'll need the bodice front, bodice back, and sleeve pieces)
Oasis bathing suit pattern (you'll need the bottom front and back pieces, following the instructions for the one-piece version with added height)
Standard sewing supplies: rotary cutter, fabric clips, thread, stretch needle

Choosing Your Size

Important tip: Cut the top and bottom pieces (excluding sleeves) from your swim lining first and baste them together to check the fit before cutting your main fabric. For the bodice, I sized down one size to achieve a snugger fit. For the bottoms, I cut my usual size.

Step 1: Cutting Your Pieces

Cut the following pieces:

Bodice front: Two mirrored pieces from main swim fabric, two from swim lining
Bodice back: One from swim fabric, one from lining
Sleeves: Two from swim fabric (no lining needed)
Bottom front: One from swim fabric, one from lining
Bottom back: One from swim fabric, one from lining

The Oasis pattern recommends adding 3 inches of height for the one-piece version. I initially cut this amount, but reduced it to 2.5 inches after basting and testing the fit.

Step 2: Assembling the Bodice

Begin by sewing the front bodice pieces to the back bodice piece at the shoulders. Complete this step for both the lining pieces and the main swim fabric pieces separately.

Instead of adding a neckband, we'll sew the lining directly to the main fabric along the neckline. Place the lining and main fabric right sides together. Baste this seam before sewing and attaching elastic. Once basted, attach elastic along the neckline on the main swim fabric side, stretching it slightly (about 10%).

After attaching the elastic, flip the pieces so right sides face out and topstitch the elastic to prevent the lining from showing through. Now, treat the lining and main fabric as a single layer. Baste them together at the sides and bottom to keep them aligned during the construction process. Sew the side seams next. A serger works well for this step due to potential bulk, but a sewing machine with a stretch stitch will also work. Place front and back pieces right sides together and stitch the sides.

Once the side seams are complete, insert the sleeves following the South Shore pattern instructions. Your bodice is now finished!

Step 3: Constructing the Bottoms

Sew the front and back pieces of the main fabric together at the crotch seam and side seams. Repeat this process for the lining pieces. Place the main fabric piece right side in, inside the lining piece (which should be right side out), creating a fabric sandwich.

Step 4: Attaching Bottoms to Top

Place the completed bodice inside the bottom piece, matching the front bodice to the front of the bottoms. Clip in place and sew around this seam. You can add elastic to this seam for extra security if desired.