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Half-Rectangle Triangle (HRT) Calculator

Cutting dimensions for HRT units at any finished size, using the no-special-ruler stitch-and-trim method.

HRT Cut Sizes (Stitch-and-Trim Method)

Finished Size (W×H)Cut Two Rectangles
2″×1″3"×2"
3″×1.5″4"×2-1/2"
4″×2″5"×3"
6″×3″7"×4"
8″×4″9"×5"
10″×5″11"×6"
12″×6″13"×7"

Each pair of rectangles yields 2 HRT units. Trim down to the exact finished + seam allowance size after sewing and cutting apart — this method deliberately oversizes the cut, unlike a true half-square triangle.

How to Sew Half-Rectangle Triangles

  1. 1. Cut two contrasting rectangles at the oversized size from the table above.
  2. 2. Layer right sides together, matching the outer edges.
  3. 3. Draw a diagonal line corner to corner on the top rectangle.
  4. 4. Sew a scant 1/4″ from the line on both sides.
  5. 5. Cut apart on the drawn line — you now have 2 HRT units.
  6. 6. Press the seam, then trim each unit to the exact finished size plus 1/4″ seam allowance on all sides using a square-up ruler.

Shop Fabric for HRT Blocks

High-contrast solids or tone-on-tones make the diagonal read clearly.

Solid Quilting CottonConnecting Threads Color Wheel Solids — 100+ colorsShop now →Precut Bundles & Fat QuartersFat Quarter Shop — every current collectionShop now →Custom Fabric by the YardSpoonflower — pick a print or design your ownShop now →

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Frequently Asked Questions

What size do I cut fabric for half-rectangle triangles?

Using the stitch-and-trim method (no specialty ruler), cut two rectangles 1" larger than the finished size in both directions. For a finished 4"×2" HRT, cut two 5"×3" rectangles. This yields 2 HRT units per pair, trimmed down after sewing.

How do I sew half-rectangle triangles?

Layer two contrasting rectangles right sides together. Draw a diagonal line from one corner to the opposite corner. Sew 1/4" from the line on both sides, then cut apart on the drawn line. Press the seam open or to one side, then trim each unit down to its exact finished size plus seam allowance using a square-up ruler — this step removes the excess from the oversized cut.

Why is HRT cutting less precise than half-square triangles (HST)?

An HST is cut from a square, so the diagonal is a perfect 45° line and the math reduces to one clean add-7/8" formula. An HRT is cut from a non-square rectangle, so the diagonal isn't 45° and the seam allowance doesn't reduce as neatly — the stitch-and-trim method compensates by cutting oversized and trimming to the exact size afterward, at the cost of some fabric waste.

Should I use a specialty ruler for HRTs instead?

If you're making many HRTs at one size, a specialty ruler (e.g. a rectangle/HRT-specific ruler) cuts closer to the finished size with far less trimming waste and no drawn line needed. The stitch-and-trim method in the table above needs no special tools and is the better choice for a one-off block or trying HRTs for the first time.