An important concept in sewing is the warp and the weft. The warp refers to the woven threads of a fabric that run lengthwise, parallel to the selvages. The weft refers to the threads that run widthwise, perpendicular to the selvages. For a more in depth explanation check out the warp and weft Wikipedia entries.

To get the proper width you need to cut off the selvages of the fabric. This creates a problem because it's hard to cut a straight line over such a long (2-1/4 yard) length of fabric. The only way to do it and still have the curtain hang nice and straight is to pull a thread up along the length of the fabric and use it as a cutting guide.

These curtains will be 40-inches wide finished so you will cut the fabric to 42-inches wide to account for the doubled 1/2-inch hems on both sides. Fold the fabric in half the long way, selvage to selvage. Measure from the middle fold out towards the selvages and make a pencil mark 21-inches from the fold (you will be about 6-inches from the selvages).

Cut from the selvage to a little past the pencil mark and draw another mark directly below the first one, on the other side of the fabric.

Now for the pulling. With your tweezers pick one WARP thread at the raw edge near the first pencil mark and pull it.

Pull the thread until it breaks. As you get going you'll be able to pull longer and longer distances, so don't be discouraged if you can only pull a few inches in the beginning.

This pulled line is absolutely straight!

Using scissors, cut along, but not beyond, the line created by the pulled thread.

Next pick another warp thread along this line and repeat. Do this along the entire length of the fabric. Repeat for the other side of the fabric (starting on your second pencil line). This process takes a while and it can be a little frustrating (especially at first) but just try to keep in mind that you're making something that will hang beautifully and look very neat and finished.

Once both selvages are cut off fold the fabric lengthwise again. Fold the fabric as straight as possible, with the weft threads at a 90 degree angle from the warp threads (the warp threads will be truly straight from the long cut edge because you cut it using the pulled thread as a guide.) Square up your end using your rotary cutter and ruler (visit our Rotary Cutting Tutorial if you need some help with this). Measure 72-inches from this cut edge (try to be as exact as possible!) then square up and cut off the other raw end. 

Repeat this whole process for the three remaining pieces of fabric (the other outer panel and the two lining panels.) 

You will have 4 pieces that are 40-inches x 72-inches. 

Update on June 18, 2008 by purl bee

These curtains will be 40"X 68.5". If you'd like to make yours a different length you can easily do so: Figure out how long you want your finished curtain. Subtract 3" from this (for the tabs) the resulting number is the length of your main curtain panel. Add 6.5 (for seam allowances) to this number and that is how long you should cut your fabric. Here's an example:

If we want a curtain with a  90" length:

90" - 3"(the length of the tabs) = 87" (the finished length of the main curtain panel)

87" + 6.5"(for seam allowances)=   93.5"- This is the length we should cut our fabric

You could also adjust the lengths of the tabs to your own specifications using the same equation but just substituting the 3" for whatever length you like.