Goal: compute cutting square size for Half Square Triangle units and related measurements.
- Unfinished unit size (before sewing into the quilt):
unfinished = finished + 2 × seam - Two at a time: starting square size per fabric:
cut = finished + 0.875 + oversize(rule of +7/8") - Eight at a time (magic 8): starting square size per fabric:
cut = 2 × finished + 1.75 + oversize - Centimeters:
cm = inches × 2.54
These provide practical cutting sizes widely used by quilters. Oversizing supports trimming for accuracy.
- Choose your finished unit size.
- Select your construction method.
- Optionally add oversize for trimming, and confirm the seam allowance.
- Set a quantity and preferred units.
- Click Calculate to see cutting squares and yardage-friendly counts.
- Use Download CSV or Download PDF to save the table.
Tip: For ultra-precise units, oversize by 0.125" to 0.25" and trim to the exact unfinished size.
| Finished size (in) | Method | Seam (in) | Oversize (in) | Cut square per fabric (in) | Unfinished size (in) | Units per two squares |
|---|
1) What is an HST unit?
An HST unit is a square made from two right triangles sewn along the diagonal, commonly used in quilting patterns.
2) Why add 7/8 inch for two at a time?
The extra 7/8" accounts for the diagonal seam and minimal trimming, producing two units from a pair of squares.
3) What does unfinished size mean?
It is the size of the unit before joining into a block. It equals the finished size plus two seam allowances.
4) Can I oversize and trim?
Yes. Add 1/8" to 1/4" as oversize, then trim to the recommended unfinished size for crisper points.
5) Which method should I choose?
Two at a time is simple for small batches. Eight at a time is efficient for many identical units.
6) How many units do I get per pair of squares?
Two at a time yields 2 units per pair. Eight at a time yields 8 units per pair.
7) Can I work in centimeters?
Yes. Switch units to centimeters to see metric equivalents based on 2.54 cm per inch.