Seam Allowance Calculator ✂️
Calculate cutting size from finished size by adding seam allowance. Standard quilting uses 1/4" seam allowance. Enter finished dimensions to get cut dimensions.
How to Use the Seam Allowance Calculator
Enter the finished dimensions of your quilt piece (the size it will be after sewing into the quilt). Enter your seam allowance — standard quilting is 1/4" (0.25"). The calculator adds the seam allowance to all sides.
The cutting size = finished size + (2 × seam allowance). For example, a 3" finished square with 1/4" seam allowance requires a 3.5" cut square.
Consistent 1/4" seam allowances are critical in quilting. Use a 1/4" presser foot or mark your seam line with tape on your machine. A few threads off on each seam compounds over a large quilt.
Frequently Asked Questions
What is the standard seam allowance for quilting?
The standard quilting seam allowance is 1/4" (0.25"). This is added to all sides of each piece, so the cutting size = finished size + 0.5" (1/4" on each side). For example, a 3" finished square requires a 3.5" cut square.
Why is a precise 1/4" seam allowance so important?
In quilting, small errors compound over many seams. A seam that's just 1/16" off adds up to 1" of error over 16 seams. Consistent 1/4" seams ensure your blocks come out the correct size and fit together properly.
How do I sew a consistent 1/4" seam?
Use a 1/4" presser foot (also called a quilting foot) on your sewing machine. Alternatively, place a piece of masking tape on your machine's throat plate exactly 1/4" from the needle as a guide. Test your seam allowance by sewing a test strip and measuring.
What is a scant 1/4" seam?
A scant 1/4" seam is slightly less than 1/4" — typically 1-2 threads narrower. Many quilters use a scant 1/4" to account for the thread and fabric take-up when pressing seams. If your blocks consistently come out too small, try a scant 1/4" seam.