Fat quarters are 18"x22" precut quilting fabric pieces. If you don't have any fat quarters, you can simply cut any fabric of your choice to size. You can also adjust the width and length of the fabric to fit the size of your onesies. I used 9-month for this project.
Read on after the jump for the full photo tutorial.
What you need:
Fat quarter or 18"x22" fabric piece
Sewing machine or needle and thread
1. Cut the fabric in half length-wise to get two 22"x9" pieces
2.Place both pieces of fabric together with the right sides facing each other. Sew a straight stitch along the widths of the two fabric pieces with a 3/8" seam to form a tube.
3. Press the seams open.
4. Hem the BOTTOM EDGE of the tube. Do this by folding 3/8" from the edge of the tube upwards twice and sewing a straight stitch along the edge.
5. Sew a basting stitch along the TOP EDGE of the tube. To do this, set the thread tension on your machine to "0", select the highest stitch length (mine was 4mm) and simply sew a straight stitch all along the edge. Next, pull on the top stitch to create ruffles. Adjust the ruffles until the width of the tube fits the width of the onesie. Knot the threads to hold the ruffles. Now you have the skirt!
6. Measure 5" from the armpits of the onesie and mark a horizontal line across. Turn the skirt inside out and place the onesie inside skirt. Match the ruffled edge of the skirt to the horizontal line. Make sure the skirt is upside down, with the bottom edge of the skirt pointing to the top of the onesie as shown.
7. Pin the skirt in place, making sure to match the side seams of the skirt to the side seams of the onesie. Sew the skirt to the onesie with a zigzag stitch. DO NOT sew a straight stitch. A zigzag stitch will allow the skirt to stretch with the onesie.
8. Turn the skirt downwards and press the seam to set it in place so that the skirt stays down.
And you're done!