Pinwheel Block Calculator 🌀
Calculate HST cutting sizes and fabric yardage for pinwheel quilt blocks. Enter finished block size and block count to get exact cut sizes for both fabrics.
How to Use the Pinwheel Block Calculator
Enter your finished block size and how many pinwheel blocks you need. The calculator uses the 2-at-a-time HST method, which produces 2 HST units from each pair of squares sewn together.
Cut equal numbers of squares from Fabric A (light) and Fabric B (dark). Layer one A and one B square right sides together, draw a diagonal line, sew 1/4" on each side, cut apart, press, and trim to the exact HST size.
Arrange 4 HSTs with the light triangles rotating around the center to form the pinwheel. Press all seams toward the darker fabric and nest the center seams for a flat, accurate intersection.
Frequently Asked Questions
How is a pinwheel block constructed?
A pinwheel block is made from 4 Half-Square Triangle (HST) units arranged so the diagonal seams radiate from the center, creating a spinning windmill effect. Each HST finished size = half the finished block size.
What is the cutting size for pinwheel HSTs?
Using the 2-at-a-time method: HST cut size = (finished block size ÷ 2) + 0.875". For an 8" finished block, each HST finishes at 4", so cut squares at 4.875".
How much fabric do I need for a pinwheel quilt?
Each block requires 2 squares of Fabric A and 2 squares of Fabric B (using 2-at-a-time HST method). The calculator adds 10% for waste. For a standard throw with 12 blocks, expect about 0.75–1 yard per fabric.