A QuiltPlan piecing guide
Half-Rectangle Triangles
Long triangles, with their points kept.
A rectangle split corner to corner into two long triangles of different fabrics. It looks like a stretched half-square triangle, but two things are different: the seam does not run corner to corner once it is trimmed (it runs through the finished unit's corners, a quarter inch in), and it leans one way only, so the unit and its mirror image are cut on different diagonals.
What you cut, for one unit
Shown for a unit that finishes 2″ × 4″. Every size is in the chart below.
| Finished unit | Rectangles, cut 1 of each | Trim the unit to | The seam meets the short end |
|---|---|---|---|
| 1″ × 2″ | 2″ × 4″ | 1½″ × 2½″ | ⅛″ |
| 1½″ × 3″ | 2½″ × 5″ | 2″ × 3½″ | ⅛″ |
| 2″ × 4″ | 3″ × 6″ | 2½″ × 4½″ | ⅛″ |
| 2½″ × 5″ | 3½″ × 7″ | 3″ × 5½″ | ⅛″ |
| 3″ × 6″ | 4″ × 8″ | 3½″ × 6½″ | ⅛″ |
| 4″ × 8″ | 5″ × 10″ | 4½″ × 8½″ | ⅛″ |
Cut 1″ wider and 2″ longer than finished for a unit twice as tall as it is wide (always 1″ over across the narrow side, and the same proportion along the long side). Less than that leaves a gap: the long seam takes about a quarter inch off each long side. The last column is a check, measured in from the corner on the trimmed unit's short ends.
Before it is sewn into anything
A 2″ × 4″ unit measures 2½″ × 4½″ before it is sewn in. Its seam runs through a point a quarter inch in from each of two opposite corners: those are the corners of the finished unit. On the short ends it meets the edge ⅛″ in from the corner. Sewn in with a quarter inch seam, each triangle's point lands right on the seam.
Making it
1 · Cut, both the same way
Cut a 3″ × 6″ rectangle of each fabric. Lay both right side up and cut each from its top left corner to its bottom right corner. Cutting them the same way, and not turning either over, is what makes every unit lean the same way.
2 · Pair and sew
Take the Fabric A triangle from below its cut and the Fabric B triangle from above its cut. Turn B over onto A, right sides together, long edges matched end to end: they are the same edge, so they match exactly. Sew a quarter inch in from it. The long edges are bias, so pin and do not stretch them.
3 · Press
Open it out and press the seam toward the darker fabric, setting it first and pressing straight down rather than sliding the iron. It is a little big, with a small step at each end: that is the fabric the trim takes off.
4 · Trim it to 2½″ × 4½″
Mark two points on a ruler a quarter inch in from opposite corners of a 2½″ × 4½″ rectangle, the corners the seam slants between. Lay the ruler with both points on the seam and trim two sides. Turn the unit, line the cut edges up with the 2½″ × 4½″ lines, put the points back on the seam and trim the other two.
5 · Check it
It measures 2½″ × 4½″. The seam runs through both quarter inch points and meets each short end ⅛″ in from the corner, not at it. If it runs right into the corner, the trim was lined up like a half-square triangle and the points will be lost.
6 · The other lean
A half-rectangle triangle cannot be turned over to lean the other way: its mirror image is a different unit. Cut those rectangles from the top right corner to the bottom left instead, and make it the same way.
Good to know
- An eighth or a quarter? Some guides say the seam lands an eighth in from the corner, some say a quarter. Both are right: it passes through points a quarter inch in from two corners, and for a unit twice as tall as it is wide that puts it an eighth in along the short end.
- Two at a time? Two rectangles laid right sides together at an angle make one unit of each lean in a single pass. Use it when a block needs both; this way is for a block that needs them all leaning the same way.
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