The following is another cropped cardi from H&M. I actually love it very much, but I couldn't fit into a size 32 by any means (didn't know why I'd get it...), thus I decided to give it a new look.
You can see how adorable those golden glitters are on the cardi... However, I am gonna give it a cruel cut!
I am using the fabric covering the bottom 3 buttons, given my desired width of the belt and my waist measurement. A cropped cardi is ideal for this project because the bottom part of it is very close to my waist measurement.
Place the fabric on the floor as follow. Leave around 1.5cm at the top and bottom parts of the fabric and draw 2 horizontal lines (i.e. red lines in the picture). Fold the fabric into half, with right side hiding. Sew the 2 red lines together securely.
After sewing the red lines, you will see a fabric tube with its wrong side facing you. Flip the fabric tube over with the right side facing you instead (as follow).
Cut out one of the sleeves and hoop around the fabric tube.
NOTE: I keep the buttons and the button holes intentionally because they can be good "buckles" of the belt. You can hide the buttons by adjusting the hoop on the belt.