How to Cover a Window Seat Cushion With Fabric & Welting

Measure the height, width and depth of the window cushion. Cut two panels 1 inch wider and deeper than the cushion; call these A panels. Cut two panels 1 inch wider and taller than the cushion; call these B panels. Cut two panels 1 inch deeper and taller than the cushion; call these C panels. The extra inch added to each dimension accounts for seam allowance.

Put one B panel and one C panel together. Line up one of the height edges of the B panels with one of the height edges of the C panel with the right sides of the fabric together. Sew those edges together with a 1/2-inch seam allowance. Repeat with the other B and C panels.

Open each B and C pair like a book. Put the pairs together with right sides facing each other. Line up the B panel of one pair with the C panel of the other pair and vice versa. Sew the pairs together with a 1/2-inch seam allowance along the short edges. This creates a square loop of fabric for the sides of your cushion's cover.

Put welting around the edges of both A panels against the right side of the fabric by lining up the flat edge of the welting with the edge of the panel. Start in the middle of one side, and work your way around pinning as you go. Fold the ends at a 90-degree angle off the edge of the fabric so the corners of the fold butt up against each other.

Sew the welting to both A panels with a 1/4-inch seam allowance, removing the pins as you go. This holds the welting in place while you sew the cushion cover together.

Line up the edges of the square loop with the edges of one of the A panels so the wrong side of both pieces face out. Line up the seams of the loop with the corners of the panel. Pin the edges together. Sew the edges together with a 1/2-inch seam allowance to create a box shape with an open top. Attach the other A panel over the open top leaving one of the short edges open.

Turn the cover right side out through the open edge. Stuff the cushion in through the opening, lining up the corners of the cushion with the corners of the cover.

Turn the edges of the fabric in 1/2-inch along the opening, and slip stitch it closed with needle and thread to complete the cushion.