Measure the distance between the two corner posts at the foot of the bed and then at the side. Double both measurements for the working widths.
Lay the curtain fabric right side up with one of the cut ends facing you. The cut ends are the width ends of the fabric.
Measure up 16 inches from the cut end of the curtain fabric, which is the curtain length plus seam allowances. Mark the spot with tailor’s chalk. Place a yardstick parallel to the cut end at the 16-inch mark. Measure from the fabric’s left edge to the working width for the foot of the bed from Step 1, and then mark the width with your chalk.
Cut the fabric to your chalk-marked dimensions from Step 3. You’ll have a piece of fabric measuring 16 inches long by the bed foot’s working width. Repeat with an identical piece for the head of the bed. If the working width is wider than the fabric width, divide the former by the latter. The result is the number of pieces -- called widths -- you’ll need to cut and stitch together to achieve the working width.
For example, if the working width is 90 inches and the fabric is 36 inches wide, you’ll need 2.5 widths of fabric, each measuring 16 inches in length. Cut the first two pieces across the full width of the fabric, and then cut a third piece 18 inches wide.
Divide the working width for the bed’s side from Step 1 by the curtain fabric width. The result is the number of pieces you’ll need to cut across the fabric’s width to total the working width. Cut that number of pieces for both sides of the bed, and cut each piece 16 inches long.
Repeat Steps 2 through 5 with the curtain lining fabric. You can use the same fabric you’ve used for the curtain face or opt for a contrasting lining.
Pin the curtain fabric pieces for the bed’s foot together end to end, with right sides together. Straight stitch the pieces together on your sewing machine. Sew with a 1/2-inch seam allowance. You’ll end up with one long piece measuring 16 inches long by the working width. Repeat with the fabric pieces for the head of the bed and both sides.
Repeat Step 7 with the lining fabric pieces for the foot, head and both sides of the bed.
Lay the curtain fabric for the foot of the bed right side up. Lay the lining fabric for the foot right side down on top of it with the edges aligned. Pin and machine sew the pieces together, using a 1/2-inch seam allowance and a straight stitch. Sew around all four sides, but leave an 8- to 10-inch opening on one side.
Clip the point from each corner of the sewn curtain panel one-quarter inch from the stitching. Turn the curtain right side out and iron it. Tuck the raw edges of the opening inside the panel, and sew the opening closed by hand.
Repeat Steps 9 and 10 with the fabric for the head and both sides of the bed.
Hand sew curtain rings -- sized and finished to go with your rod or rails -- to the tops of the curtain panels. Sew one ring to each end of each panel. Space the rest of the rings 5 to 7 inches apart.
Remove the rods from their hooks or brackets for wooden beds with curtain rods attached to the canopy frame. Slide the rings onto the rods and then reattach the rods to the bed. For thin-railed canopy beds made of wood or metal, unscrew the finials at the tops of the posts. Remove the rails one at a time, and slide the curtain rings onto the rails. Replace the rails and screw the finials back on the posts.