Turn blocks 45° and every measurement runs through √2: a 10 in block spans 14⅛ corner to corner, and the edges need side and corner triangles cut so their straight grain faces out. All of it, from your block size and grid.
Your On-Point Layout
Your Quilt
56 ⅝ × 70 ¾in
4 × 5 blocks of 10″ on point
Assemble in diagonal rows, a setting triangle capping each end; corners last. Cutting the triangle squares ⅛–¼ over and trimming the finished top floats the points safely.
- Block diagonal14.14 in
- Setting triangles14, from 4 squares at 15 ½″ (both diagonals)
- Corner triangles4: from 2 squares at 8″ (one diagonal)
- Alternate plain squares, if used12 at 10 ½″
The Formulas
diagonal = block × 1.414 · quilt = blocks across × diagonal, by blocks down × diagonalsetting triangles: square = block × 1.414 + 1¼, cut both diagonals · corners: square = block ÷ 1.414 + ⅞, cut onceBoth triangle rules exist for grain: setting triangles are quarter-squares so their long side, the quilt’s edge, stays straight grain; corners are half-squares for the same reason. Cut them the “wrong” way and the quilt’s whole perimeter is bias.
Worked Example
Twenty 10 in blocks set on point, 4 × 5:
- Diagonal: 10 × 1.414 = 14.14 in → quilt 56⅝ × 70¾.
- Setting triangles: 14 side gaps → squares at 10 × 1.414 + 1¼ = 15½ (cut 4 from each) → 4 squares.
- Corners: four, from two squares at 10 ÷ 1.414 + ⅞ = 8 in, each cut once diagonally.
- Plus 12 plain setting squares at 10½ if alternating, the classic on-point look.
On-Point Chart
| Block | Diagonal | Setting triangle square | Corner square |
|---|---|---|---|
| 4″ | 5.66″ | 7″ | 3 ¾″ |
| 6″ | 8.49″ | 9 ¾″ | 5 ⅛″ |
| 8″ | 11.31″ | 12 ⅝″ | 6 ⅝″ |
| 10″ | 14.14″ | 15 ½″ | 8″ |
| 12″ | 16.97″ | 18 ¼″ | 9 ⅜″ |
Assembling Diagonal Rows
- Rows run diagonally: each row is blocks (and setting squares) capped by a setting triangle at each end; corners go on last.
- Count the gaps: a grid x across and y down needs 2(x−1) + 2(y−1) side triangles and 4 corners, the calculator counts them for your grid.
- Oversize habit: many quilters add ⅛–¼ to both triangle squares and trim the assembled top straight: “floating” the blocks slightly inside the edge.
Assumptions and Defaults
- Straight (non-staggered) on-point set; alternate plain squares are the usual filler and cut at block + ½.
- Setting-triangle squares yield four each, corner squares two each.
- Sizes land on the nearest ruler ⅛, rounded up.
On-Point Questions, Answered
How big is my quilt block when set on point?
A block set on point spans its diagonal, which is the block size × 1.414, so a 10 in block measures about 14⅛ in on point. That extra span is why on-point quilts grow so quickly: five diagonal rows of 10 in blocks already pass 70 in.
What size are on-point setting triangles?
On-point setting triangles are quarter-square triangles cut from a square at the block size × 1.414 + 1¼ in, which is 15½ in for a 10 in block, giving four triangles per square. Cut this way, the long edge of each triangle runs on the straight grain and faces the quilt’s outer edge.
What size are the corner triangles for an on-point quilt?
The corner triangles for an on-point quilt are half-square triangles cut from squares at the block size ÷ 1.414 + ⅞ in, which is 8 in for a 10 in block, using two squares cut once each. They follow the same grain logic as the side triangles, keeping the quilt’s corners on the straight grain.
Why do the edges of my on-point quilt wave?
The edges of an on-point quilt wave when the triangles were cut with bias along the outer edge, or when exactly cut triangles stretched during assembly. Cut by the rules above, handle the edges gently, and consider cutting the triangles oversize so you can trim the edges straight at the end, which fixes most waves.