Making a slipcover for a sectional with back pillows involves sewing a separate cover for each piece in the sectional. This may take a little extra work to complete, but the slipcover will fit better and allow you to move the sectional pieces without taking off the covers. The attached pillows will fit comfortably underneath the slipcover as long as you hold the measuring tape loosely over the top of the pillows when taking the body measurements.
Sketch a picture of each sectional piece so you can note the measurements as you take them.
Measure the body width of each sectional piece by placing a measuring tape on the floor in front and following it along the shape of the pieces to the floor in back. Avoid pulling the measuring tape tight along the surfaces so you get an accurate measurement of the cushions and pillows. Increase the actual measurements by 12 inches for the seams and tucking.
Determine the body length of each sectional piece by placing the measuring tape on the outside edge of one arm and stretching it across the sectional piece to the other side. Increase the actual measurements by 12 inches for the seams and tucking.
Measure the width of the sectional sides from the back edge to the front edge. This measurement should be the same for each piece. Increase the actual measurement by 2 inches for the seams.
Determine the length of the sectional sides by placing the measuring tape on the side at the floor and taking the measurement to the start of the seat cushion. Measure over the arm for sectional pieces that include an armrest. Increase the actual measurements by 2 inches for the seams.
Draw a picture of the slipcover for each piece, using the measurements taken. You will have one large body piece from the measurements taken in Steps 2 and 3 and two side pieces from the measurements taken in Steps 4 and 5.
Cut the slipcover pieces from the upholstery fabric so there are three pieces for each section. Lay the large body piece of fabric onto the sectional piece and push the excess fabric into the rear cushion crack so the front and rear edges are at floor level. Lay the side pieces in the appropriate location and pin them to the edge of the body piece so the right sides are together.
Remove the fabric from the sectional and sew the sides to the body with a 1/2-inch-wide seam. Lay the fabric back on the sectional so the wrong side faces up and tuck in the excess fabric. Pin together the rear and front edges and sew them together with a 1/2-inch-wide seam.
Fold the fabric along the bottom edge 1/4-inch to the wrong side of the cover. Fold the fabric another 1/4-inch to create a clean edge and sew along the first folded edge to finish the hem.