Y-Seam Calculator 💎
Calculate cutting sizes for Y-seam (set-in seam) blocks including 60° diamonds and Tumbling Blocks. Get strip width, diamond length, and 3-color fabric yardage.
How to Use the Y-Seam Calculator
Enter the finished size of one diamond side and the number of Tumbling Blocks you need. The calculator gives you the strip cut width and diamond cut length for 60° diamonds.
Cut fabric strips to the strip width, then use a 60° ruler to cut diamonds at the diamond length. The three colors (dark, medium, light) create the 3D cube illusion in Tumbling Block quilts.
Y-seams require stopping your stitch at the seam allowance dot, not at the fabric edge. Practice on scrap fabric first. Press seams carefully — Y-seams can distort if pressed incorrectly.
Frequently Asked Questions
What is a Y-seam in quilting?
A Y-seam (also called a set-in seam) is a seam where three fabric pieces meet at a single point, forming a Y shape. Y-seams are used in 60° diamond blocks, Tumbling Blocks, and other complex geometric patterns.
How do I cut 60° diamonds for quilting?
Cut strips at the diamond width (finished size + seam allowances), then cut diamonds at the calculated length using a 60° ruler. The strip width = finished size + 2×seam allowance; diamond length = finished size × 1.1547 + 2×seam allowance.
How many colors does a Tumbling Block pattern need?
The classic Tumbling Block pattern uses 3 colors (dark, medium, and light) to create a 3D cube illusion. Each block needs one diamond of each color — so for 12 blocks you need 4 diamonds of each color.