Calculating how much fabric you need to make a quilt is easy once you understand the basics. Try this step-by-step tutorial to calculate yardage for your next quilting project. Choose a Quilt Size and Design First You’ll need to make some decisions before you can calculate how much fabric is needed for a quilt:
Figure out how large the quilt will be, keeping standard mattress sizes in mind
Decide how much of the quilt top will be made up of quilt blocks, and how much of its size will be taken up by borders and/or sashing
Make a rough sketch on paper or use computer software to draw the quilt What quilt block size will you use? How many blocks will it take across and down to fill the space within the quilt? For instance, for a quilt that measures about 60 inches x 80 inches, six 10 inch blocks across and eight 10 inch blocks down will fill the space, requiring 48 blocks. Be sure to add fabric for borders if you plan to use them, and decide if borders will be cut along the fabric’s straight grain or crosswise grain. Will blocks be straight set or placed on point? Multiply the block’s finished size by 1.41 to determine the width an on point block will occupy in the quilt. Will you use plain setting triangles for on point quilts? You can piece partial blocks to use as setting components, but if you don’t, you’ll need two types of triangles to fill in the jagged edges. Triangles look the same but are cut differently. Decimal to Fraction Conversions A conversion chart is handy for yardage calculations.
Divide the finished size of the block, 9 inches, by the number of rows across or down, three. The answer, 3 inches, is the finished size of each of the nine grids.
All nine grids in this block contain half-square triangles, and we must add 7/8 inch to the finished size of a half-square triangle to calculate its cut size, making seam allowances.
Each block has three dark blue 3 7/8 inch half-square triangles: we’re making 20 blocks, so multiply that by three per block, making 60 triangles. We can cut two triangles by dividing a 3 7/8 inch square once diagonally as shown.
The 60 triangles divided by the two each square yields means 30 squares are required.
Most quilting fabric has a usable width of about 40 inches, often a bit more. Divide 40 inches by 3 7/8 inches, the size of your squares. The answer, 10.32, is the number of 3 7/8 inch cuts you can make across the width of the fabric. Slide that back to a whole number, 10 cuts.
Now divide 30 (the required number of squares) by 10 (the cuts you’ll make per strip), making strips required to cut the squares, assuming no waste.
Multiply three strips by 3 7/8 inch (the width of each strip) to make 11 5/8 inch, the total length of fabric required to cut three strips.
A yard of fabric is 36 inches long, so divide the length of fabric required, 11 5/8 inches, by 36 inches. The answer is .32 yard (refer to the decimal conversions on page 1 if necessary). Bump up the yardage to compensate for errors or shrinkage during pre-wash–in this case, 1/2 yard.
20 triangles divided by 2 (the number that can be cut from a 9 7/8 inch square) = 10 squares required
40 inch width of fabric divided by 9 7/8 inches = 4.05, or 4 squares per strip
10 squares required divided by 4 per strip = 2.5, or 2 strips plus about a half strip, each 9 7/8 inches wide.
9 7/8 inches x the 3 required cuts (even though one need be a partial width) = about 30 inches of fabric.
30 inches divided by 36 inches (yard) = .83 yard, bump up to 1 yard to allow for shrinkage and provide a bit of excess for squaring up. Follow the same procedure for each part of the block, adding together yardages for like fabrics. Quilt Border Yardages Borders help you easily adjust the size of your quilt top. Vary the number of borders you sew to the quilt, or adjust their widths to suit you. Once you’ve determined widths and styles, it’s easy to calculate border yardage. Keep in mind that mitered borders require longer strips than butted borders. Sashing Yardage Calculate yardage for sashing and cornerstones as you would for any other unit in the quilt. Make a rough sketch of the quilt layout to help you visualize how many strips are required.
Sometimes It’s Necessary to Change the Size of a Quilt Block It’s easy to change the size of most quilt blocks once you understand patchwork quilt block structure. I’ll explain a few of the most critical points here, but recommend that beginning quilters read a detailed description of patchwork basics before scaling a block up or down. Explanations of four popular quilt block layouts:
A four-patch quilt block is made up of four square grids, two across and two down (left illustration).
A nine-patch quilt block is made up of nine-square grids, three across and three down (middle illustration).
Five-patch (right illustration) and seven-patch (not shown) quilt blocks are a bit different because their names describe how many square grids exist in a single row across or down, not the total number of grids in the quilt block. Four-patch and nine-patch quilt blocks are routinely sub-divided to create more intricate patterns, but once you become a block watcher it will be easy to identify their underlying structure. Five-patch and seven-patch block grids can be sub-divided into multiple patch units, but that isn’t quite as common, other than the use of half-square triangles because the grids are usually a bit small already. Keep in mind that individual grids in a quilt block are sometimes combined, rather than subdivided, like the areas created by red strips in the five-patch block above right. Why should you care about quilt block structure? Once you can decipher a quilt block’s grids, you can make it larger or smaller with ease. And although structure is important for altering the size of a quilt block, it’s also a huge component when designing a quilt, because some blocks just don’t ‘mesh’ when sewn side-by-side, even if they’re the same size. You’ll learn more about that in my patchwork structure tutorial. Always make a test block in the new size before cutting all of your fabric. Some Blocks Require Different Methods for Size Alterations Some quilt blocks are easier to scale using different techniques. An eight-pointed star made with diamonds (versus the ‘cheater’ version with half-square triangle units) and some blocks with curved patches (which are sometimes more difficult to draw correctly) are two examples. If you find a block that isn’t easy to alter using the methods in this tutorial, make a photocopy, enlarging or reducing the block to the finished size you wish to sew. Measure the sizes of its patches (remembering that the dimensions are unfinished). Use templates to construct the block or refer to my patchwork shape cutting instructions to choose a patch and block size that can be easily rotary cut (remember that all shape sizes must be altered in the same way).