A Time to Sew Quilt Designs
by

Cheryl Almgren Taylor


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Although quilting is one of the most creative and fun things you can do, sometimes it is necessary to make mathematical calculations, especially if you like to design your own patterns. Listed on this page is some useful information that can be referred to when you are feeling math challenged.

Yardage Measurements Fat Quarters Quilt Dimensions On Point Blocks
Decimal Conversions Side Setting Triangles Common Setting Triangle Sizes


Yardage Measurements

Fabric is usually purchased "by the yard", 36 inches, or a fraction of a yard. Fabric is traditionally manufactured in 44" widths; however, recently some manufacturers have shortened that to 42". These measurements explain what the length of the fabric cut is when you buy a fraction of a yard.

Yardage 1/8 1/4 3/8 1/3 1/2 5/8 2/3 3/4 7/8 1
Inches 4.5 9 13.5 12 18 22.5 24 27 31.5 36




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Fat Quarters

Normally 1/4 of a yard of fabric would be a piece that measured 9" x 44". Quilters use a special cut of fabric called a "fat quarter". It results in the same area of fabric, but the yardage has been cut differently so that the piece measures 18' x 22", enabling quilters to cut larger pieces than you could from a regular quarter of a yard of fabric.  
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Quilt Dimensions

There are variations in what determines the appropriate size for a bed quilt. When determining how big you want your quilt to be, you must first know the dimensions of your mattress. These are listed below.
Standard Mattress Sizes

Crib Mattress: 28" x 52"
Twin/ Single Mattress: 39" x 75"
Full/ Double Mattress: 54" x 75"
Queen Size Mattress: 60" x 80"
King Mattress: 76" x 80"
California King: 72" x 84"
Next you must know how far you want the quilt to come down on the side of the bed. This is called the "drop". A quilt needs at least a 12" drop on each side and the bottom if you want it to cover the side of the mattress and you need to add an additional 15" to the top edge if you want to cover the pillow. If you want the quilt to serve as a full-size bedspread with a 21" drop on each side, the chart below lists common sizes.

Twin / Single Full / Double Queen King
81" x 110" 96" x 110" 102" x 115
120" x 115

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On Point Blocks

Blocks that are arranged "on point" are rotated so that the square block is laid out in a diamond effect. While this is a beautiful layout, it creates some mathematical complications when designing a quilt. This is because the diagonal measurement of the block is creating the width. To determine this measurement, you simply multiply the finished block size by 1.41. For example, 6" square block no longer has a 6" width on the quilt top, but has a width of 8 1/2".

The chart below gives diagonal measurements for a number of common block sizes.

Finished Block Size 1" 2" 3" 4" 5" 6" 8" 10"
Diagonal Measurement 1-1/2" 2-7/8" 4-1/4 5-5/8" 7-1/8" 8-1/2 " 11- 3/8" 14-1/8"







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Decimal Conversion

Sometimes quilt making requires that we cut pieces with strange, fractional measurements. Knowing the fractional equivalent in decimals can be a help. The following chart provides decimal equivalents for a number of common fractions used in cutting quilt pieces.

Fraction 1/8 1/4 3/8 1/2 5/8 3/4 7/8 1
Decimal .125 .25

.375

.50 .625 .75

.875

1.0

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Corner Setting Triangles

Corner setting squares are made from half square triangles. That means that a square block has been cut on the diagonal, resulting in two triangles. The legs of the triangle form the outside edge of the quilt and the hypotenuse is sewn to the block edge. There are two formulas that can be used to make corner setting triangles.

Formula #1 has you divide the finished block size by 1.414; then add .875 for the seams, and round up to the nearest 1/8". The square block would be cut this size and then cut corner to corner with one diagonal cut, resulting in two corner triangles.

Formula #2 has you multiply the finished block size by 1.41 and divide that answer by 2. Then add .875 for seams and round up to the nearest 1/8". Cut a square block this size and then make one diagonal cut, corner to corner, resulting in two corner triangles.

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Side Setting Triangles

Side setting triangles are used along the side a quilt with on-point block layout. They are made by cutting a square twice diagonally, resulting in 4 triangles. The legs of the triangles are on the bias and the base is on the straight of grain, thus it goes on the outside of the quilt top.

The formula for figuring side setting triangles is to multiply the finished block size by 1.414, add 1.25 to this measurement, and then round up to the nearest 1/8". This is the size to cut the square block, which will then by crosscut diagonally twice, resulting in 4 triangles.

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Common Setting Triangle Sizes

This chart lists the sizes of squares that will be cross cut to create setting triangles.

Finished Block Size
Side Triangle Squares
Corner Triangle Squares
4"
7"
3-3/4"
5"
8-3/8"
4-1/2"
6"
9-3/4"
5-1/8"
7"
11-1/4"
5-7/8"
8"
12-5/8"
6-5/8"
9"
14"
7-1/4"
10"
15-1/2"
8"
12"
18-1/4"
9-3/8"
14"
21"
10-3/4"













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E-mail: cheryl@atimetosewquilts.com