Formula
Two at a time adds 7/8 inch, or 1 inch when you plan to trim. Four at a time uses the diagonal: finished size × √2 + 1¼ inch, then up to the next 1/8 inch. Eight at a time is twice the finished size plus 1¾ inch. Each set is two squares, one of each fabric. If the quantity is not a full set, the count rounds up.
2-at-a-time = finished + ⅞ in
4-at-a-time = finished × 1.414 + 1¼ in
8-at-a-time = 2 × finished + 1¾ in
geese large = width + 1¼ in
geese small = height + ⅞ in
These additions are the seam allowances quilters use for those methods. They assume a ¼ inch seam and, for the four-at-a-time size, a trim. A different seam allowance changes the square.
Worked examples
Eight 4 in half-square triangles, two at a time. Squares are 4.875 in. Four sets, so four squares of each fabric, and you make eight.
Four 3 in units, four at a time. 3 × 1.414 + 1.25 is about 5.49 in, which rounds up to 5.5 in. One set: one square of each fabric.
Four flying geese, finished 4 in wide by 2 in tall. One 5.25 in square and four 2.875 in squares.
Reference
Cut size for a 4 inch finished half-square triangle, and for a 4 × 2 inch goose. One full set.
| Method | Square | Squares per set |
|---|---|---|
| 2 at a time | 4.875 in | 2 (one of each) |
| 2 at a time, trim | 5 in | 2 (one of each) |
| 4 at a time | 7 in | 2 (one of each) |
| 8 at a time | 9.75 in | 2 (one of each) |
| Geese, large | 5.25 in | 1 |
| Geese, small | 2.875 in | 4 |
Questions
What size square makes a 4 inch half-square triangle?
Two at a time, the squares are the finished size plus 7/8 inch, so 4.875 inches. Add a full inch instead, 5 inches, if you want room to trim. You need one square of each fabric for every two units. Eight units are four squares of each.
How does four-at-a-time differ?
Each square is the finished size times 1.414, plus 1¼ inch, rounded up to the next 1/8 inch. Two squares, one of each fabric, make four units. The 1.414 is √2, the diagonal of the finished square.
What squares do no-waste flying geese use?
Four geese at a time: one large square at the finished width plus 1¼ inch, and four small squares at the finished height plus 7/8 inch. A 4 by 2 inch goose is a 5.25 inch large square and 2.875 inch small squares.
Sources
- Two-at-a-time: finished + 7/8 in, or finished + 1 in to trim. Four-at-a-time: finished × √2 + 1¼ in, up to 1/8 in. Eight-at-a-time: 2 × finished + 1¾ in.
- No-waste flying geese, four at a time: large = finished width + 1¼ in; each small = finished height + 7/8 in. Quantity rounds up to a full set.