Formulas
2-at-a-time: square = finished + 0.875". 4-at-a-time: square = (finished + 0.5") ÷ 0.64 (bias edges—trim). 8-at-a-time: square = 2×finished + 1.75". Yield per fabric pair is 2, 4, or 8 HSTs respectively.
Worked example
40 finished 3" HSTs with 8-at-a-time: square 7.75"; 5 pairs (10 squares) produce 40 HSTs. Same batch 4-at-a-time: square ≈ 5.47"; 10 pairs. Same batch 2-at-a-time: square 3.875"; 20 pairs.
Tips
Trim HSTs to exact unfinished size (finished + 0.5") after pressing. Starch helps bias edges—especially on 4-at-a-time units.
Common mistakes
Using unfinished size in a finished-size formula; skipping the trim step; using finished + 1" for 4-at-a-time (that undercuts the usual published formula).
Trimming and pressing
Press HSTs toward the darker fabric or open if bulk is an issue. Use a square ruler to trim to unfinished size (finished + ½"). Chain-piecing speeds 2-at-a-time methods. When mixing methods in one quilt, keep unfinished sizes identical so blocks nest cleanly.
Limits and how to use the results
Estimates run only in your browser. Prefer a published pattern’s tested yardage when it conflicts with this planner. Density factors and assumptions are documented on the methodology page; legal terms cover planning-use limits.
Unfinished sizes and block math
Quilters often talk about unfinished HST size, which is finished + ½". If a block pattern says “make 3.5" unfinished HSTs,” that is a 3" finished triangle unit. Convert before using the finished-size formulas in this tool. When a block mixes HSTs with squares, keep all units on the same unfinished grid so seams nest. Label stacks by size when cutting multiple finishes in one sitting.
FAQ
What size squares for 3" HSTs?
3.875" for 2-at-a-time; about 5.47" for 4-at-a-time; about 7.75" for 8-at-a-time.
Which method should I use?
2-at-a-time for a few HSTs or precise grain; 4-at-a-time for speed (trim bias edges); 8-at-a-time for large matching batches.