Straight Binding is made using either the straight of grain or cross-grain strips of fabric.
To determine how much straight binding is needed for your project, measure the length and width of your quilt top. Double that number and add about 14" . These extra inches allow room for making mitered corners and make finishing the ends easier to accomplish.
For example: Let's say I have a quilt top that measures 68.5 inches x 80.5 inches. In order to calculate the total length of binding needed, I would write 68.5 + 80.5 x 2 = 298 inches. Then, I add 14 inches to that for working ease. 298 + 14 = 312. So, I need binding that is 312 inches in length.
Also, I need to decide if I'm going to use a single-fold strip or a double-fold strip. A single-fold is less strong than a double-fold. I would only use a single-fold if it were for a wall hanging that would receive very little wear and tear. A double-fold strip is strong and can hold up to many washings. I pretty much use double-fold or French binding exclusively.
Next, I determine how wide I want the finished binding to be. The size I use most often is a finished 3/8 inch binding. I just like the look of that size. Since my binding is to be folded double, I need to double all of my width measurements. Usually, a 1/4" seam is used to sew the binding onto the quilt top. I like to add a smidgeon extra because I believe some of the width is taken up in the folding of the fabric over itself and over the edges of the quilt.. So, I take 3/8" for the top, 3/8" for the back and 3/8" for the seam allowance. Then I double that. 3/8 + 3/8 + 3/8 = 1 1/8. 1 1/8 x 2 = 2 1/4. So I will cut my strips 2 1/4" wide.
Most fabric is 42" to 44" in useable width. I count on the lesser measurement of 42" when calculating how many strips to cut by width of fabric. That way I don't risk running short.
To have enough binding to cover the edges of my quilt, I need to cut 8 strips by width of fabric. Cutting by the width of the fabric allows a little bit of "give" to the binding and just makes it easier to work with.
Sew the strips together by laying two strips right-sides-together and perpendicular to one another. Sew a diagonal line as shown.
Press the seam open.
Trim seam to 1/4".
Continue adding strips in this manner until all strips have been joined.
Press binding in half length-wise.
It is now ready to be sewn onto your quilt.