Determine what size dog pillow you want to make and cut two fabric rectangles in the dimensions you decide. A small dog pillow could be approximately 21 inches by 16 inches, a medium pillow would be 29 inches by 22 inches, large would be 34 inches by 29 inches and extra large would be 39 inches by 33 inches (a 1-inch seam allowance is included in each dimension).

Place the two fabric rectangles together with the right sides facing each other. Match up the corners and sides and pin the two rectangles together to secure the pieces.

Begin stitching the pillow together using a 1/2-inch seam allowance 3 inches away from one corner. Stop stitching when you are 1/2 inch away from the edge of the corner and pivot the sewing machine needle 90 degrees to turn the corner. Continue stitching around three sides and three corners. Stop stitching 3 inches after the last corner. Remove the pillow from the sewing machine.

Fold over 1/2 inch of both the top and bottom fabric of the pillow along the opening. Iron these folds to create a finished edge along the opening.

Turn the dog pillow right side out through the opening you didn't sew. Pull each corner out to make a sharp corner.

Fill the dog pillow with fiberfill until it is as firm or as soft as you want. Make sure the fiberfill reaches into all four corners.

Thread the needle with a 15-inch length of double thread. Hand stitch the opening closed with the needle and thread using a whip stitch.