Trimming Your Quilt
After quilting, the sides of your quilt may be slightly different in length. You can equalize the difference by measuring through the middle of the quilt both horizontally and vertically, and using these measurements (plus seam allowances) when figuring the binding length on each side.
You may wish to trim the quilt until the sides are equal, but if the amount you're trimming is significant, keep in mind that you may alter the proportion and balance of the borders. You may also alter the difference between the quilting motifs and the quilt edge from one border to the next.
To begin squaring up your quilt, it's best to lay your project on a rotary-cutting mat on a flat surface.
Position a large acrylic square ruler in one corner of the quilt, aligning adjacent edges of the ruler with adjacent edges of the quilt top. Place a long acrylic ruler above the square ruler, aligning the long edge with the quilt top edge. Using a rotary cutter, cut away the batting and backing that extend beyond the quilt top edge. Reposition the rulers and cutting mat as needed to trim around the entire quilt.
If you do not wish to rotary-cut the excess batting and backing, mark the cutting line along the ruler edge, and then use scissors to trim on the line.