Sophie from Roubidou created this shirt onesie for all of the little ones attending summer garden parties, weddings and more. The original was designed for her baby cousin so he could look smart on occasions without being burdened by numerous layers of clothes, and “so that his little chubby legs can still enjoy the feeling of grass and the warm tickling of the sun!” Be sure to look at Sophie’s Roubidou (full of lots of wonderful sewing for her baby girl, due this fall) and don’t miss her introduction. Happy Summer Sewing!


  • one large shirt
  • all-purpose thread to match fabric + to match buttons
  • normal sewing foot + buttonhole foot or attachment for your machine
  • water-soluble fabric-marking pen or chalk
  • hand-sewing needle
  • elastic thread
  • small safety pin
  • interfacing for the collar
  • bias-tape maker
  • shirt onesie pattern, size 3-6 months

1. Lay out and cut pattern.

2. Cut pieces ~ One men’s shirt will give you ample fabric to work with. I essentially followed the man’s shirt; the back of the shirt is the back of my onesie, the sleeves become the sleeves of my onesie, etc. Very handily you don’t have to bother sewing a button placket, just use the one of the shirt. I wanted my placket to be asymmetrical, but if you want a more classical look, just lay the front pattern at the middle of the placket. I cut the sleeves just below the cuff to benefit from the button placket there as well– practical and pretty. For the facing of the collar and the bias binding I used a contrasting fabric. You’ll need a yard (a bit less than one meter) of bias binding for this project. If you’re new to bias bindings check out Dana’s tutorials.

3. Back of the shirt ~ Iron two pleats in the middle of the back, so that both back pieces of the shirt have the same width. Sew both pieces together right sides facing.

4. Sew shoulder seams ~ Sew the shoulder seams together with a flat felled seam. You can find a tutorial here. It’s not difficult and the seam will be more durable and have a nice, clean finish. Alternatively, you could just attach the shirt front and the shirt back at the shoulders, right sides facing, sew them together, and press the seams open.

5. Sew sleeves ~ Turn and press the sleeve hem to the right side and then turn and press the edge again to the right side. Topstitch the double-folded edge and repeat with the second sleeve. Next, with right sides facing, sew one sleeve to the armhole of the joined front and back piece. Repeat with second sleeve. Try to ease the curve of the sleeve onto the armhole. Clip the curved seam allowances and press toward the wrong sides.

6. Sew shirt and sleeve side seams ~ Right sides facing and edges aligned, sew the sleeves and the shirt’s side seams together.

7. Bottom bias ~ Hem the bottom of the shirt with a bias-bound finish. At the same time, the bias binding will be the tunnel for the elastic, so leave it open at both ends. Next you’ll insert the elastic and thread it through the bias tunnel using a safety pin. Experiment a bit with the length of the elastic thread and sew it in place when you think it’s short enough. I attached the thread by threading the elastic on a needle and then I sewed it firmly in place with a couple of stitches on the inside of the shirt. If you are using an elastic band instead of thread, just sew it in place with a few zig-zag stitches.

8. The collar ~ Iron interfacing on the wrong side of one of your collar pieces. Then sew the two collar pieces together right sides facing, stitching along the raw outer curve so the inner edge will stay open. Turn the collar right side out and press it. Then turn the shirt and pin the collar with its right side facing the wrong side of the shirt’s neck opening. Sew the collar onto the shirt. Turn the shirt again to the right side and give the raw seam of the collar a bias-bound finish.

9. Almost there! ~ Now all you have to do is sew two buttonholes about one inch apart from one another onto the back side of your shirt. One of the matching buttons should be the last button of the shirt’s front placket. If there isn’t one, sew a button plus buttonhole onto the placket. Sew on a second button corresponding to the second back side buttonhole.

This pattern should be easily scaled up for larger sizes; just use a larger onesie as a guide. If a simple shirt is too plain for you, you could add pockets or embroider something onto it.

Following the same basic pattern I made a version with short, ruffled sleeves.

And for festive summer occasions you might want to sew matching mini bow-ties or shoes.