Measure the width of the window and multiply by two. Measure the height of the window from the bottom of the curtain rod to the top of the radiator and add five inches. This is the measurement for your drape and lining panel.
Cut your fabric to size. Trim 4 inches off the side of the lining fabric and 1 inch off the length.
Place your drape fabric and lining right sides together. Align the fabrics along each side and pin a 1/2-inch seam allowance. Sew a 1/2-inch seam on each side, stopping 2 1/2 inches from the bottom of the drape fabric. Turn the fabric right side out. Center the lining on the drape fabric with the lining side up. The lining will overhang the drape 2 inches on each side. Iron the sides.
Fold the top fabric to the back 1/2 inch and iron. Fold the fold to the back 2 inches and sew a hem stitch attaching the fold to the fabric.
Fold the bottom drape fabric to the back 1/2 inch and iron. Fold the fold to the back 2 inches and pin. Attach your drape to the curtain rod and check your length. The drape should be 1/2 to 1 inch above the radiator. Adjust your pins to correct the hem. Take the drape down and sew with a hem stitch.
Fold the lining fabric along the bottom to the back 1/2 inch and iron. Fold the fold to the back 2 inches and pin. Hang your drape and check your lining hem. The lining should be shorter than the drape hem. Adjust your pins and sew a hem stitch attaching the lining to the lining fabric.