Calculating the right amount of quilt backing fabric is a crucial step in finishing your quilt. Too little, and you're scrambling for more fabric that might not match; too much, and you've wasted money and created unnecessary stash. This guide, along with our handy calculator, will help you determine exactly how much backing you need, accounting for all the important factors.
Quilt Backing Calculator
Why Accurate Backing Calculation Matters
The backing of your quilt is more than just the fabric on the other side; it's an integral part of the quilt's structure and aesthetic. Getting the calculation right ensures a smooth quilting process, whether you're sending it to a longarmer or quilting it yourself on a domestic machine. Running short mid-project is a frustration no quilter wants!
Key Factors in Backing Calculation
Before you even touch the calculator, understand the variables:
- Quilt Top Dimensions: The finished width and length of your quilt top. Measure carefully!
- Backing Fabric Width (WOF - Width of Fabric): Standard quilting cotton is typically 42-44 inches wide. Wide backing fabric can be 90, 108, or even 120 inches wide.
- Buffer/Oversize: You always need more backing than your quilt top. This extra fabric allows for squaring up, potential shrinkage during quilting, and provides ample space for your longarmer's frames or for maneuvering on a domestic machine.
- Seam Allowance: If you need to piece your backing (which is common for larger quilts with standard width fabric), you'll need to account for the seam allowance where strips are joined.
Step-by-Step Guide to Calculating Quilt Backing
Step 1: Measure Your Quilt Top Accurately
Lay your finished (or almost finished) quilt top flat and smooth. Measure the width and length in at least three places for each dimension and average the measurements. This accounts for any slight inconsistencies in piecing.
Step 2: Add a Buffer for Quilting
It's standard practice to add extra inches to both the width and length of your quilt top to determine the needed backing size. A common recommendation is to add 8-10 inches to both the width and the length of your quilt top. Our calculator uses 8 inches as a safe baseline.
- Why 8-10 inches? This provides 4-5 inches of extra fabric on each side, which is essential for:
- Squaring up the backing fabric before loading.
- Allowing for minor shifting or stretching during the quilting process.
- Providing space for longarm machine clamps or for gripping on a domestic machine.
- Accommodating any slight shrinkage that might occur.
Example: If your quilt top is 60" x 72", with an 8" buffer, your target backing size is 68" x 80".
Step 3: Consider Your Backing Fabric Width (WOF)
The width of the fabric you choose is critical. Standard quilting cotton (44/45 inches) often requires piecing for anything larger than a baby quilt. Wide backing fabrics (90, 108, 120 inches) are designed to avoid piecing for most common quilt sizes.
Step 4: Determine How Many Strips You'll Need (If Piecing)
This is where it gets a little tricky, as you want to orient your fabric efficiently to minimize waste and seams. You have two main options when piecing standard width fabric:
- Seams Parallel to Quilt Length: You cut strips that are the buffered length of your quilt. You then join these strips along the buffered width.
- Seams Parallel to Quilt Width: You cut strips that are the buffered width of your quilt. You then join these strips along the buffered length.
The goal is to choose the orientation that requires the least amount of total fabric. Our calculator automatically determines the most efficient layout for you.
When piecing, remember to account for seam allowances. If you're joining two pieces with a 1/2-inch seam allowance, you effectively lose 1 inch of width for every seam (0.5 inch from each piece). Our calculator subtracts 1 inch from the fabric width for each seam if piecing is required.
Step 5: Calculate Total Length in Inches
Once you've determined the optimal orientation and number of strips, multiply the number of strips by the length of each strip (which will be either your buffered quilt width or buffered quilt length, depending on orientation). This gives you the total inches of fabric you need to purchase.
Step 6: Convert to Yards
Fabric is sold by the yard. Divide your total inches by 36 (since there are 36 inches in a yard) to get the total yards needed. It's always a good idea to round up to the next full or half yard to be safe, especially if the calculation is very close to a whole number.
Example Calculation Walkthrough
Let's say your quilt top is 60 inches wide by 72 inches long, and you're using standard 44-inch wide fabric.
- Add Buffer:
- Buffered Width: 60" + 8" = 68"
- Buffered Length: 72" + 8" = 80"
- Usable Fabric Width (for piecing): 44" - 1" (for seams) = 43"
- Option A (Strips are 80" long, seams parallel to quilt length):
- Strips needed: Ceil(68" / 43") = Ceil(1.58) = 2 strips
- Total inches: 2 strips * 80" = 160 inches
- Option B (Strips are 68" long, seams parallel to quilt width):
- Strips needed: Ceil(80" / 43") = Ceil(1.86) = 2 strips
- Total inches: 2 strips * 68" = 136 inches
- Choose Optimal: Option B requires 136 inches, which is less than 160 inches.
- Convert to Yards: 136 inches / 36 inches/yard = 3.77 yards.
You would need to purchase approximately 3.75 to 4 yards of fabric, cut into two 68-inch strips, to back this quilt.
Tips for Success
- Buy Extra: When in doubt, buy a little more than you calculate. It's better to have a bit left over for future projects or mistakes than to be short.
- Pre-wash Backing Fabric: Especially if your quilt top fabrics were pre-washed, pre-wash your backing to prevent differential shrinkage.
- Directional Prints: If your backing fabric has a directional print, ensure you orient your strips correctly when piecing so the design runs in the desired direction.
- Wide Backing Fabric: For larger quilts, consider using wide backing fabric (90" or 108" wide) to avoid piecing altogether. This saves time and ensures a seamless look.
- Longarmer Requirements: If you're sending your quilt to a longarmer, always check their specific requirements for backing size, as some may have slightly different buffer recommendations.
With these guidelines and the calculator, you're well-equipped to confidently prepare your quilt backing for your next masterpiece!