Experts say that a weighted blanket should typically be 10% of your body weight
Materials for filling a weighted blanket:
plastic poly pellets
micro glass beads
dried beans/grains/stone
DIY Weighted Blanket Materials
Fabric for front and back of blanket
Weighted filling (typically beads or pellets)
Batting
Kitchen scale
Ruler
Pins
Thread (preferably matching to your blanket)
Scissors
Sewing machine
Steps for making a weighted blanket:
Step one — Take both the front and back panels of your blanket. Arrange them so that the front sides of both panels are facing each other, and the back of the panels are facing outward. Line up the corners so they match perfectly and pin on the four corners.
Step two — Take your batting and line it up with your blanket on both sides. Pin all around the border, about an inch into the fabric and batting.
Step three — Sew it up on three sides. We recommend leaving it open on a shorter side of the blanket. After the blanket is sewn up, flip it inside out.
Step four — From here, you’ll need to make vertical lines with the opening at the top. How many lines your create will depend on how many squares you want. If you want your blanket to have 16 squares (4×4), you’ll need to sew three lines, to make four columns.
Step five — Next, measure out your weighted filling per square. If you’re unsure how much weight per square, reference the Blanket’s Weight section above. Fill each column with one squares worth of filling. Then, pull the blanket up so that all the beads fall to the bottom of your blanket and then pin out one row, creating a row of squares. Sew the row up.
Step six — Repeat this step until all your squares are filled and sewn up, and then sew up the edge to seal the blanket completely.
Step seven — Trim any loose ends and enjoy your new weighted blanket!
Sources: https://myslumberyard.com/blog/how-to-make-a-weighted-blanket-diy/