Pinwheel Block Calculator
Zero Waste & No Sign-up: Calculate HST cutting sizes for pinwheel quilt blocks. Enter your finished block size to get precise square dimensions for both fabric pieces.
How to Use the Pinwheel Calculator
Enter the finished pinwheel block size and the number of blocks. Each pinwheel is built from four half square triangles whose finished size is half the block — a 6-inch pinwheel uses four 3-inch HSTs spinning around the center.
Cutting sizes follow the two-at-a-time HST method: starting squares are the HST finished size plus 7/8 inch, so the 6-inch block starts from 3-7/8 inch squares. Every pair of squares (one of each fabric) yields two HSTs, which means each block consumes two squares of fabric A and two of fabric B.
From the square count the calculator estimates yardage for both fabrics based on 44-inch-wide fabric, adds a 10 percent cutting margin, and rounds up to the next eighth of a yard. Twelve 6-inch blocks, for example, need twenty-four 3-7/8 inch squares of each fabric. For scrappy pinwheels, keep the background fabric constant and vary only the spinning triangles: the fabric A estimate still holds while fabric B spreads across your scrap bin.
Frequently Asked Questions
How many HSTs make a pinwheel block?
A standard pinwheel block uses four Half Square Triangles (HSTs) arranged so their diagonal seams create a spinning pinwheel effect. Two contrasting fabrics are used, two HSTs of each.
How do I make a pinwheel block spin the right way?
Arrange the four HSTs so that the darker triangle rotates clockwise (or counterclockwise) around the center. Press all seams consistently to reduce bulk at the center point.
What is the nesting seam technique for pinwheels?
Press the HST seams in alternating directions so the seam allowances 'nest' together where the four blocks meet at the center. This reduces bulk and creates a flatter intersection.