Figuring the Vertical Repeat:
If you plan to use a fabric with a printed design, you will need to match the design when you join two widths together. First you must determine the height of the pattern repeat which is called a vertical repeat. Simply measure from the top of the design in one spot down to the same spot in the design below. That distance will be the vertical repeat.
Keep in mind that the pattern on all windows in a room should match.
Cutting the Panels:
After you have figured your vertical repeat, you need to determine the cut length of all of your widths.
For example, lets say you want the finished length of your panels to be 90 and your fabric has a vertical repeat of 27. Using the formula below you will see that your cut lengths will need to be 108 to allow for the repeat.
90 (finished length) divided by 27 (repeat) = 3.33
Round 3.33 up to 4
4 is the number of repeats you will need:
4 x 27 = 108 (cut length)
When matching most pattern repeats, your cut length will be longer than you actually need. You will have to trim the excess length away. So based on the example above, you will have to trim off 18. However, it is best to sew the widths together first and then trim the panels to your desired length.
Cut and sew your widths together, making sure you match the vertical pattern. Most decorative fabrics are made so that the pattern matches at or just inside the selvage. If you line up the pattern on each width of fabric at the selvages (right sides together) and stitch right along or just inside the selvage, the pattern should match.
You may trim the excess from the bottom or the top of the panels. Remember, if you have more than one window in the room, you need to cut all of your panels at the same place.