Quilt sashing is the strips of fabric placed between quilt squares to hold them together. The width and color of the sashing strips is determined by the quilter. Although squares can be connected directly to eachother, sashing adds an elegant touch to a quilt. It is often used to emphasize the patterns within the quilting squares.
Things You'll Need
 Paper
 Pencil
 Calculator
 Quilt square
 Yardstick or tape measure

Draw a diagram of the quilt on a piece of paper. Make sure to include the proper amount of quilt blocks. Separate the blocks with an area indicating the sashing placement. For example, if the quilt is three blocks wide by five blocks long, draw a diagram with three blocks across and five blocks down, leaving a space between each block. In the space around the outside edge of the blocks, draw a frame around the quilt. The total number of vertical sashing strips needed is four and the total number of horizontal sashing strips is six.

Determine the desired width of your sashing. For example, a 2inch sashing requires a 3inch strip of fabric. This allows for a 1/2inch seam on each side of the strip to connect the quilt's squares.

Measure the length and width of the quilt square. Write the dimensions onto the quilt diagram your drew earlier. For example, if the quilt square is 12inches by 12inches. Write 12 inches along each edge of one quilt block on the paper diagram.

Determine the amount of fabric for one horizontal sashing by multiplying the number of squares across the horizontal axis of the quilt by the square's width. Then, multiply the number of vertical strips by the width of the sashing strips. Add these two numbers together. Multiply the number of horizontal sashing strips by the width of the sashing.
Using our example: The squares are 12inches wide. There are three squares along the horizontal axis of the quilt. Multiply 12 by 3. You'll need 36 inches of fabric to span the length of the quilt blocks. There are 4 vertical strips. The width of each vertical strip is 3 inches. Multiply 3 by 4. You will need an additional 12 inches to span the width of the sashing strips. Add 36 plus 12 for a total of 48 inches. Each horizontal strip requires a lengh of fabric 48inches long by 3inches wide. You need six horizontal strips total, so you need at minimum of 48inches by 18inches of material.

For the vertical quilt sashing, you will not be cutting long strips. Instead, you need several smaller strips that will fit between the horizontal sashing. On your diagram, count the number of vertical squares and multiply that by the length of the squares. Using our example above, you have five vertical squares that are 12inches in length, so you need 60inches of fabric to border these squares. Count the number of vertical strips between the squares and multiply that by the width of the sashing. Using our example, there are four vertical strips and the sashing is 3inches wide. So, you need 60inches by 12inches of fabric for your vertical sashing.
References
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