Setting triangle calculator
For 10″ finished blocks set on point, cut side setting triangles from 15 1/2″ squares (cut twice on the diagonal) and corner triangles from 8″ squares (cut once). Enter your block size and layout to get the triangles, the block count and the finished size.
Setting triangle chart
Cut sizes rounded up to the next ⅛″, with centimetres under each. Side triangles: 4 from each square. Corner triangles: 2 from each square, and a quilt always needs 4.
| Finished block | Block on point (diagonal) | Side triangles: cut square | Corner triangles: cut square |
|---|---|---|---|
| 3″ | 4 1/4″ | 5 1/2″14.0 cm | 3″7.6 cm |
| 4″ | 5 5/8″ | 7″17.8 cm | 3 3/4″9.5 cm |
| 5″ | 7 1/8″ | 8 3/8″21.3 cm | 4 1/2″11.4 cm |
| 6″ | 8 1/2″ | 9 3/4″24.8 cm | 5 1/8″13.0 cm |
| 7″ | 9 7/8″ | 11 1/4″28.6 cm | 5 7/8″14.9 cm |
| 8″ | 11 3/8″ | 12 5/8″32.1 cm | 6 5/8″16.8 cm |
| 9″ | 12 3/4″ | 14″35.6 cm | 7 1/4″18.4 cm |
| 10″ | 14 1/8″ | 15 1/2″39.4 cm | 8″20.3 cm |
| 11″ | 15 1/2″ | 16 7/8″42.9 cm | 8 3/4″22.2 cm |
| 12″ | 17″ | 18 1/4″46.4 cm | 9 3/8″23.8 cm |
| 14″ | 19 3/4″ | 21 1/8″53.7 cm | 10 7/8″27.6 cm |
| 16″ | 22 5/8″ | 24″61.0 cm | 12 1/4″31.1 cm |
Quilt size for common on-point layouts
Finished centre before borders, the number of full blocks, and how many side triangles to cut.
| Block | Across × down | Centre size | Full blocks | Side triangles |
|---|---|---|---|---|
| 8″ | 4 × 5 | 45 1/4″ × 56 5/8″ | 32 | 14 (4 squares) |
| 8″ | 6 × 7 | 67 7/8″ × 79 1/4″ | 72 | 22 (6 squares) |
| 10″ | 3 × 4 | 42 3/8″ × 56 5/8″ | 18 | 10 (3 squares) |
| 10″ | 4 × 5 | 56 5/8″ × 70 3/4″ | 32 | 14 (4 squares) |
| 10″ | 5 × 6 | 70 3/4″ × 84 7/8″ | 50 | 18 (5 squares) |
| 12″ | 3 × 4 | 50 7/8″ × 67 7/8″ | 18 | 10 (3 squares) |
| 12″ | 4 × 5 | 67 7/8″ × 84 7/8″ | 32 | 14 (4 squares) |
| 12″ | 5 × 6 | 84 7/8″ × 101 7/8″ | 50 | 18 (5 squares) |
Why squares cut on the diagonal
Setting triangles sit on the outside of the quilt, so their long edge should be on the straight grain and not stretch. Cutting a square twice on the diagonal puts the straight grain on the long side of the side triangles; cutting a square once puts it on the two short sides of the corner triangles, which form the corners of the quilt. Want a little float around the blocks? Cut the squares 1″–2″ larger and trim after the top is sewn.
Making the blocks from triangles? The HST calculator has cut sizes for 2, 4 and 8 at a time. Formulas: how we calculate.
Learn it by doing: How an on-point quilt goes together, animated.
Questions quilters ask
What size setting triangles for a 10 inch block?
Cut side setting triangles from 15 1/2 inch squares, cut twice on the diagonal (4 triangles per square), and corner triangles from 8 inch squares, cut once on the diagonal (2 per square). That keeps the straight grain on the outside edge of the quilt.
How do you calculate setting triangles?
Side triangles: block diagonal (finished block × 1.414) + 1 1/4 inch, cut twice diagonally. Corner triangles: finished block ÷ 1.414 + 7/8 inch, cut once diagonally. Round up to the next 1/8 inch. Many quilters cut a little larger still and trim the edge after the top is together.
How many setting triangles do I need?
For a layout of A blocks across and D blocks down: 2 × (A − 1) + 2 × (D − 1) side triangles and always 4 corner triangles. A 3 × 4 layout needs 10 side triangles (3 squares) and uses 18 full blocks.
How big is a quilt with blocks set on point?
Each block measures its diagonal across the quilt: finished block × 1.414. A 12 inch block is 17 inches corner to corner, so 3 blocks across make a centre about 51″ wide before borders.
Updated 2026-11-14.
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