This self-lined bandeau bikini is super simple to make. It's only made of 4 rectangles and doesn't use very much fabric. I was able to make it with 1/4 meter each color. This bandeau could easily cost less than $10, or maybe even free if you have some scrap fabric laying around!

Step 1: Gather Your Supplies

bathing suit material or jersey
tape measure
scissors
pins
matching thread
sewing machine

Step 2: Measure and Cut

Measure:

1st Measurement:

Measure around the fullest part of your bust. (Eg. 34 inches)

2nd Measurement:

Take the 1st Measurement and divide that number in half. Add about an inch to that number for seam allowance. (Eg. 34/2 + 1 = 18 inches)

3rd Measurement:

Measure how much vertical coverage you want. Add about an inch to that number for seam allowance. (Eg. 6 + 1 = 7 inches)

4th Measurement:

Take the 3rd Measurement and add about 2 inches. (Eg. 7 + 2 = 9 inches)

Cut:

2 rectangles of fabric with the dimensions of 2nd Measurement x 3rd Measurement for the front pieces. I used 2 different colors, so I cut one rectangle of each.
2 rectangles of fabric with the dimensions of 1st Measurement x 4th Measurement for the back pieces.
I used 2 different colors, so I cut one rectangle of each.

Make sure you cut your fabric so that the stretch is going lengthwise. You may want to cut out paper pattern pieces first to make sure you have the correct measurements.

Step 3: Sew Front Pieces

For sewing with stretchy fabric, a zig-zag stitch should be used. Your sewing machine might have a stitch for stretchy fabric, so you could use that instead.

Fold one of the front pieces in half with the good sides touching and pin. Sew both sides until 1 inch from the fold. Turn right side-out.

Pull the second front piece through the hole created in the first piece. Match the edges on one side of the piece that was pulled through the hole with the good side of the fabric touching and pin. Sew along the edge and get as close as you can to the fold. Do the same with the other side and then turn right side-out.

Step 4: Sew and Attach Back Pieces

Individually fold each of the back pieces with the good sides touching. Pin and sew, creating open-ended tubes.

Baste the open edge of the front pieces. You can do this using a long stitch with the sewing machine or by hand. Pull the threads and evenly space the gathers created.

Stuff the whole front piece into one of the back piece tubes and align one of the gathered edges with the edge of one end of the tube. Match the seams, pin, and sew. Pull the front piece through to the other end of the tube. This should turn everything right side out. Do the same with the second back piece.

To finish the tie ends, fold under a half and inch and sew close to the edge.