Making a dress with straps or sleeves into a strapless dress allows you to take an old dress and transform it into something new and stylish. It is a project that you can do with or without a sewing machine and can make to look as professional as an unaltered dress. It is simply a matter of removing the straps, fitting the top and carefully hiding your seams and stitches so that they blend into the original garment's pattern and form.
Seam rip the edges of the dress where the straps are attached to separate the strap material from the rest of the dress at each point where the straps connect if your dress has straps. If you have a dress with sleeves and no connecting seam, put the dress on and mark where you want the top of the dress to hit above your bust under your arms and on the back. Cut the material about a quarter of an inch above the line where you marked. If your dress has a zipper be sure that you are cutting with the zipper pulled down.
Fold any raw edges that came out when removing the straps or cutting the material under and pin them in place with the straight pins. Use a thread that closely resembles the thread that the dress was sewn with. Match the style of the stitches when sewing to create a seamless effect.
Hide the ends of your thread by pulling them through to the inside of the fabric and clipping the thread from there. This will help create a professional finished look.
Put your dress on inside out. Strapless dresses need to be more fitted than strapped dresses so that they don't fall off.
Pin your dress at both side seams so that it's snug around the top of your bust. Pin as far down the side seam as you have extra fabric to work with.
Take the dress off and mark where you have pinned. Remove the pins and use an iron to press the fabric flat where you will be sewing. This will help ensure that your fabric doesn't get twisted or misaligned when you sew it.
Reinsert the pins to keep your fabric in place. Sew a seam on each side of your dress where you have marked it until you cross over the original seam.
Turn your dress right side out and try it on. You should now have a fitted strapless dress.
If your dress has a more complicated neckline you may need to turn the top edge over while the dress is on inside out. Pin it down and sew along the entire top edge to get a consistent seam. If you end up with lumps in the seam on the side of your dress, the stitching may be uneven. Make sure that your seam is in a straight line and flows right into the existing seam of the dress to avoid these lumps.