Quilt Half-Rectangle Calculator: Half-Rectangle Triangle Cut Sizes

Work out half-rectangle cut sizes before you cut. Enter finished half-rectangle width, finished half-rectangle height and half-rectangles needed, and see cut rectangle size, pairs needed, rectangles per fabric and HRTs made, with the formula in steps.

Calculate your half-rectangle cut sizes

Finished half-rectangle width in

Finished half-rectangle height

Finished half-rectangle height is the height of one half-rectangle triangle in the finished quilt, after seams are sewn. Half-rectangle height can be any size, it does not have to be half of finished width.

Half-rectangle triangles needed

Half-rectangle triangles needed is a whole number, greater than zero. Count half-rectangle triangles by fabric pair, not by quilt, if different fabric pairs use different finished sizes.

This calculator uses the oversize and trim method only. Cut rectangles are larger than finished size on purpose, then trimmed after sewing.

This calculator uses the oversize and trim method only. Two rectangles, one of each fabric, sewn on the diagonal and cut apart, make 2 HRTs, then trim to unfinished size, which is finished size plus 1/2 inch in each direction. For half-square triangles, use the HST Calculator, or the Fabric Calculator for fabric yardage.

Your result

Enter your measurements, then calculate.

How the calculator works

Step 1: Cut rectangle size

Cut rectangle width equals finished half-rectangle width plus 1 inch, and cut rectangle height equals finished half-rectangle height plus 1 inch, for the oversize and trim method. The extra 1 inch in each direction gives room for the diagonal seam and for trimming to finished size after sewing. For finished width 4 inches and finished height 2 inches, cut rectangle size equals 5 by 3 inches.

Step 2: Pairs needed and rectangles per fabric

Pairs needed equals half-rectangles needed divided by 2, rounded up to a whole number, because each pair of rectangles makes 2 HRTs, and a partial pair cannot be sewn. For half-rectangles needed 20, pairs needed equals 20 divided by 2, equals 10 pairs. Rectangles per fabric equals pairs needed times 1, because each pair uses 1 rectangle of each fabric. For pairs needed 10, rectangles per fabric equals 10 rectangles.

Step 3: Total rectangles and HRTs made

Total rectangles equals rectangles per fabric times 2, because each pair uses one rectangle of each fabric. For rectangles per fabric 10, total rectangles equals 10 times 2, equals 20 rectangles. HRTs made equals pairs needed times 2, because each pair makes 2 HRTs. For pairs needed 10, HRTs made equals 10 times 2, equals 20 HRTs, exactly the number needed, with no extra HRT.

Assumptions, shown next to the result

This calculator uses the oversize and trim method only, with seam allowance 0.25 inch on each side, as is standard for piecing. Trimming to finished size after sewing is required, because cut rectangles are oversized by 1 inch in each direction, and they are not finished size before trimming. Cut rectangle sizes are used as entered in the unit mode you choose, with no extra added for mistakes or shrinkage, beyond the 1 inch already in the formulas. If half-rectangles needed is an odd number, pairs needed is rounded up, and HRTs made will be one more than half-rectangles needed, which is one extra HRT, not a mistake.

Half-rectangle cut size chart

This chart uses the same formulas as the calculator: cut rectangle width equals finished width plus 1 inch, cut rectangle height equals finished height plus 1 inch, for the oversize and trim method, then trim to unfinished size after sewing, which is finished size plus 1/2 inch in each direction.

Finished half-rectangle size	Cut rectangle size
2 by 1 inches	3 by 2 inches
4 by 2 inches	5 by 3 inches
6 by 3 inches	7 by 4 inches
8 by 4 inches	9 by 5 inches

Chart values are a guide for the finished sizes shown. Your own finished size may give a different result. Use the calculator above for your own measurements.

Worked example, checked against the calculator

Finished half-rectangle size 4 by 2 inches, half-rectangles needed 20.

Cut rectangle size: width 4 plus 1 equals 5 inches, height 2 plus 1 equals 3 inches, so cut rectangle size equals 5 by 3 inches, then trim to 4.5 by 2.5 inches after sewing, which is the unfinished size.

Pairs needed: 20 divided by 2 equals 10 pairs.

Rectangles per fabric: 10 times 1 equals 10 rectangles. Total rectangles: 10 times 2 equals 20 rectangles.

HRTs made: 10 times 2 equals 20 HRTs, exactly the number needed, with no extra HRT.

Frequently asked questions

How do I calculate half-rectangle triangle cut size?

For the oversize and trim method, cut rectangle width equals finished half-rectangle width plus 1 inch, and cut rectangle height equals finished half-rectangle height plus 1 inch, then trim to unfinished size after sewing, which is finished size plus 1/2 inch in each direction. For example, finished 4 by 2 inch half-rectangles need 5 by 3 inch cut rectangles.

What is a half-rectangle triangle?

A half-rectangle triangle, or HRT, is a rectangle divided on the diagonal into two triangles, with two different fabrics. Its finished size is the size in the finished quilt, after seams are sewn, for example 4 by 2 inches.

How many rectangles do I need for HRTs?

Each pair of rectangles, one of each fabric, makes 2 HRTs. Pairs needed equals HRTs needed divided by 2, rounded up to a whole number. For example, 20 HRTs need 10 pairs, 10 rectangles per fabric, 20 rectangles total, and make 20 HRTs exactly.

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