Quick Reference Chart: Setting Triangles and Setting Squares for On-Point Quilts

ThatPainter is reader-supported. When you buy through links on our site, we may earn an affiliate commission. Learn More

For an on-point quilt, begin with the block’s finished size—not its unfinished size. For side-setting triangles, multiply the finished block size by 1.414 and add 1¼ inches; cut the resulting parent square twice diagonally. For corner-setting triangles, divide the finished block size by 1.414 and add ⅞ inch; cut the parent square once diagonally. For a setting square, add ½ inch to the finished block size.

#	Preview	Product	Price
1		Quilting Rulers,Sewing Ruler,4 Piece Acrylic Square Quilting Templates,Clear Precision Ruler for...	$9.99	Buy on Amazon
2		Sewing Ruler,5 Piece Quilting Rulers,3 x17 Inch,1.5 x17 Inch,3 x12 Inch,1.5 x10 Inch,1 x6...	$9.99	Buy on Amazon
3		8 Quilting Rulers(3.5",5", 8",10",12.5",6.5"x12",2"x12",3"x9")	$18.78	Buy on Amazon
4		Quilting Rulers Sewing Ruler,Acrylic Quilting Ruler Templates,Precision Cutting Tools for Patchwork...	$9.99	Buy on Amazon
5		Quilting Rulers, 7 Piece Acrylic Ruler, Fabric Cutting Ruler (12.5"X12.5", 9.5"X9.5", 6"X6",...	$16.99	Buy on Amazon

As an Amazon Associate I earn from qualifying purchases.

Round calculated triangle sizes up to the next ⅛ inch. The chart below gives the traditional measurements for finished blocks from 1 to 20 inches and assumes square blocks, ¼-inch seams, and no additional sashing adjustment. For the publisher’s original reference, see AllPeopleQuilt’s setting-triangle and setting-square article and its official downloadable chart.

Quick chart for on-point quilt settings

Use the column that matches the finished size of your square block. The side and corner measurements are the sizes of the parent squares before they are cut into triangles. The setting-square measurement is the square’s cut size.

#1 Best Overall

Quilting Rulers,Sewing Ruler,4 Piece Acrylic Square Quilting Templates,Clear Precision Ruler for Quilting Sewing,Tools Supplies Accessories Green(3.5"x3.5" 5"x5" 6.5"x6.5" 10.5"x10.5")

• Premium Thick Acrylic Construction Made of high grade transparent acrylic material, this quilting ruler set features a sturdy, wear resistant build that resists cracking, warping and bending for long term daily use. The clear design offers full visibility of fabric underneath, while smooth polished edges protect hands and fabric from snags or damage, ideal for frequent sewing and quilting projects.
• Precise Clear and Crisp Green Markings Equipped with sharp, fade resistant green measurement markings and clear grid lines, including 1/8 inch incremental scales, 90 degree right angle and 45 degree diagonal guides for ultra precise cutting and measuring. The high contrast green scale stands out clearly on both light and dark fabrics, eliminating reading errors and ensuring flawless piecing, trimming and block squaring every time.
• Complete Multi Size Square Set Includes 4 essential square quilting rulers in 3.5", 5", 6.5" and 10.5" sizes, covering all daily quilting, sewing and fabric crafting needs. From small patchwork details and trimming tiny blocks to large fabric cutting and full quilt block finishing, this all in one set meets the demands of beginners, hobbyists and professional quilters alike.
• User Friendly and Stable Design Lightweight yet durable structure ensures easy handling and maneuverability during crafting. The flat balanced design stays securely in place when cutting with rotary cutters, no unwanted shifting or sliding. Each ruler is easy to use for all users, with easy to read numbering and clear measurement guides for hassle free operation.
• Multi Purpose Sewing and Craft Tool This versatile acrylic quilting ruler set is perfect for quilting, sewing, fabric cutting, patchwork, scrapbooking and other DIY craft projects. Compatible with all standard rotary cutters and cutting mats, it is a must have essential tool for sewing rooms, craft studios and classrooms. A practical and thoughtful gift for sewing enthusiasts, quilters and craft lovers.

$9.99

Buy on Amazon

Chart measurements are based on the formulas in the official AllPeopleQuilt reference PDF. The PDF is supplied for personal use; link to the publisher’s file rather than reposting it.

What “on point” means

A straight-set quilt places square blocks in ordinary horizontal and vertical rows. An on-point, or diagonal-set, quilt turns those blocks 45 degrees so they appear as diamonds. The blocks are sewn in diagonal rows, and the triangular spaces around the outside must be filled to create a square or rectangle.

          C
       S  B  S
    S  B  Q  B  S
       S  B  S
          C

Side-setting triangles

The larger triangles along the four sides of the quilt. They fill the spaces between the outside blocks and the straight perimeter.

Corner-setting triangles

The four triangular pieces at the corners of a conventional rectangular on-point quilt.

Setting squares

Solid, pieced, or appliquéd squares placed between focal blocks. They are optional and are not the same pieces as corner-setting triangles. Their design role is described in AccuQuilt’s setting guide.

Measure the finished block first

The formulas use the block’s finished sewn size: the size the block will occupy in the quilt after it is joined to neighboring pieces. Do not use the raw size of one unit or the unfinished size printed in a pattern.

For example, a block listed as 12½ inches unfinished normally finishes at 12 inches after the ¼-inch seam allowances are sewn. Use 12 inches in the chart or formulas.

Also do not substitute:

• the size of an individual half-square triangle, strip-set unit, or other component;
• the unfinished block measurement;
• the block’s finished diagonal; or
• the block size alone when finished sashing or cornerstones change the spacing in the layout.

The chart’s constants assume conventional ¼-inch seams. If your pattern uses another seam allowance or a construction method with different allowances, follow that pattern’s measurements or recalculate with a test section before cutting all the fabric.

The three formulas

1. Side-setting triangles

Finished block size × 1.414 + 1¼″ = side parent-square cut size

Use this parent square for the triangles along the sides. Cut the square twice diagonally, making an X. One parent square produces four side-setting triangles.

The factor 1.414 is a practical version of the diagonal factor √2. For hand calculation, 1.414 gives the chart measurements. If using a calculator, you can use 1.41421356 and then round the final answer upward to the nearest ⅛ inch.

Rank #2

Sewing Ruler,5 Piece Quilting Rulers,3 x17 Inch,1.5 x17 Inch,3 x12 Inch,1.5 x10 Inch,1 x6 Inch,Acrylic Ruler,Cutting Ruler with Non-Slip Rings (Black and White)

• This quilting ruler is made of high-quality acrylic, laser cut for a smooth edge ,3mm/0.12" thick durable enough not easy to break.
• Package includes 5 Acrylic Rulers,3 x17 Inch,1.5 x17 Inch, 3 x12 Inch, 1.5 x10 Inch,1 x6 Inch.
• 15 Pieces non slip grip rings,These Non-Slip Grips can be placed on the back of any ruler to prevent movement or sliding during cutting.
• Quilting ruler Ideal for many forms of crafts, including quilting, sewing, patch working, piecing,measuring, drawing, and crafts.

$9.99

Buy on Amazon

2. Corner-setting triangles

Finished block size ÷ 1.414 + ⅞″ = corner parent-square cut size

Use this smaller parent square for the corners. Cut it once diagonally, making two triangles. A conventional rectangular on-point quilt needs four corner triangles, so it normally needs two corner parent squares.

3. Setting squares

Finished block size + ½″ = setting-square cut size

Cut the setting square whole; do not cut it on the diagonal. The extra ½ inch represents two ¼-inch seam allowances, so the finished setting square is the same size as the finished focal block.

Worked examples

For a 3-inch finished block

• Side triangles: 3 × 1.414 + 1.25 = 5.492 inches. Round up and cut a 5½-inch square, then cut it twice diagonally. It yields four side triangles.
• Corner triangles: 3 ÷ 1.414 + 0.875 = 2.996 inches. Round up and cut a 3-inch square, then cut it once diagonally. It yields two corner triangles.
• Setting square: 3 + 0.5 = 3½ inches. Cut one whole square for each setting-square position.

For a 10-inch finished block

• Side triangles: 10 × 1.414 + 1.25 = 15.39 inches, so cut a 15½-inch parent square and cut it twice diagonally.
• Corner triangles: 10 ÷ 1.414 + 0.875 = 7.945 inches, so cut an 8-inch parent square and cut it once diagonally.
• Setting square: 10 + 0.5 = 10½ inches.

Why the two triangle types are cut differently

The diagonal cuts are not interchangeable. They put the fabric grain in different places.

For side triangles, each resulting triangle retains one original edge of the square as its long edge. That straight-grain edge belongs on the quilt’s outside boundary. For corner triangles, the two original square edges form the two short outside edges, while the diagonal edge points inward and is sewn to the quilt center.

This arrangement does not eliminate every possible source of distortion, but it gives the exposed perimeter the most stable grain direction and keeps most bias edges inside the quilt. That makes the top easier to sew, square, border, and bind. The grain-direction distinction is also explained by Generations Quilt Patterns, Quilt Bugg, and Epida Studio.

Rank #3

8 Quilting Rulers(3.5",5", 8",10",12.5",6.5"x12",2"x12",3"x9")

• Warm Tips:Please remove the film on the quilting rulers to see the number clearly.If you find the numbers printed backward on your side,please turn to the other frosted side,and pull off the film
• Quilting Rulers and Templates:Includes 5 quilting square rulers(3.5",5",8",10",12.5")and 3 quilting rulers(6.5"x12",2"x12",3"x9")to meet all your patchwork needs
• Enduring Material: These quilting rulers are made of high quality acrylic,0.3mm/0.12" thick,very sturdy
• Easy to Use:We specially create two-color scales for you,whether on light or dark material are very easy to work
• Quilting Rulers Non Slip:These Non-Slip Grips can prevent sliding during use

$18.78

Buy on Amazon

How many parent squares do you need?

Block size determines the size of each piece, but it does not determine the number of pieces. Count the actual open spaces in your planned layout.

• One side parent square cut twice produces four side-setting triangles.
• One corner parent square cut once produces two corner-setting triangles.
• A conventional rectangular on-point layout has four corner triangles, normally requiring two corner parent squares.
• For side triangles, divide the number required by four and round up to a whole parent square. Leftover triangles are expected when the count is not divisible by four.

Lay out all the blocks before cutting. Count each side opening separately, especially if the layout is rectangular, has partial blocks, includes a border, or uses an unusual arrangement. A pattern-specific cutting list overrides this general count when the pattern accounts for those details.

How to cut the pieces

1. Verify the finished measurement. Measure a sewn block if necessary. Do not trust an assumed size if your seam allowance or pressing has changed it.
2. Calculate and round up. Use the chart when the finished size is listed; otherwise calculate with the formulas and round the final triangle parent-square measurement upward to the next ⅛ inch.
3. Mark the grain. Before cutting, identify the fabric’s lengthwise and crosswise grain. The original square edges—not the diagonal cuts—are straight grain.
4. Cut side parent squares twice diagonally. Make one diagonal cut from corner to corner, then the other to form an X. A large square ruler or a carefully aligned long ruler is useful for this cut.
5. Cut corner parent squares once diagonally. This makes two half-square-style triangles. Do not use this cut for side spaces.
6. Keep each group together. Label side and corner triangles separately. If the fabric is directional, check the print orientation before making every diagonal cut.

A side triangle that is cut only once becomes a half-square-style triangle and puts a bias edge on the quilt’s exterior. That can stretch and ripple when borders or binding are added. Conversely, cutting a corner parent square twice is unnecessary and changes the resulting pieces.

Assembly sequence for an on-point quilt

On-point construction is easier when the entire design is visible rather than treated as ordinary horizontal rows.

1. Lay out the complete top on a design wall, floor, or large table. Check block orientation, setting-square placement, fabric direction, and the position of every triangle.
2. Group pieces into diagonal rows. Label rows and mark the order of blocks before moving them.
3. Add side-setting triangles to the appropriate blocks or row ends according to the pattern. The long straight-grain edge will eventually form part of the outer perimeter.
4. Add the corner-setting triangles at the four outer corners of a conventional rectangular layout.
5. Sew the diagonal rows together. Match the seams between neighboring blocks and setting pieces. Do not try to force the diagonal layout into conventional horizontal rows.
6. Press and handle gently. The inner triangle seams include bias edges. Avoid dragging or stretching the partially assembled top.
7. Square the quilt center before adding borders. Trim only after checking that the block points and outer edges are correctly positioned.

When joining a side triangle, align the relevant triangle corner with the block or row corner. Extra fabric at a tip is intentional and can be trimmed after the seam is sewn. When joining a corner triangle, center it on the row or block edge; it may extend beyond both ends. This alignment approach is demonstrated in Epida Studio’s assembly guide and Designed to Quilt’s diagonal-row instructions.

If the quilt has sashing or cornerstones

The basic chart assumes adjacent square blocks with no finished sashing changing the distance between them. With sashing or cornerstones, do not automatically plug the focal-block size into the formulas. Instead, calculate the finished distance represented by the actual layout.

1. Measure the finished block.
2. Measure the finished sashing and cornerstone dimensions—not their unfinished cutting sizes.
3. Draw or inspect the on-point arrangement and determine the finished distance from one block position to the next along the side or corner being filled.
4. Use that effective finished unit in the side or corner formula.
5. Make a small test section before cutting the entire set of triangles.

For example, a documented sashed-layout worksheet uses a 6-inch finished block. For its side calculation, a ¾-inch finished cornerstone makes an effective unit of 6¾ inches:

6¾ × 1.414 + 1¼ ≈ 10.80″

That result is cut as an approximately 11-inch side parent square. For its corner calculation, ¾ inch of finished sashing on each side makes an effective unit of 7½ inches:

Rank #4

Quilting Rulers Sewing Ruler,Acrylic Quilting Ruler Templates,Precision Cutting Tools for Patchwork Fabric,Sewing Supplies Purple(6"X17",3"X16",1.5"X12",1"X11")

• All in one 4 piece quilting ruler kit for quilting sewing patchwork fabric cutting measuring and pattern making.
• COMPLETProfessional clear permanent scales deliver precise cutting accurate patchwork and high standard craft projects.E SET:Quilting rulers, perfect for various quilting projects
• Shatter resistant durable acrylic ensures stable rotary cutting repeated use and long lasting accuracy.
• Perfect for quilt block making patchwork assembly fabric trimming DIY sewing and home decoration projects.
• Necessary quilting tools sewing supplies fabric cutting tools and accessories for hobbyists and professionals.

$9.99

Buy on Amazon

7½ ÷ 1.414 + ⅞ ≈ 6.18″

The cited Quilting Nook worksheet reports a 6⅜-inch corner parent square for that project. If you apply the strict “round upward to the nearest ⅛ inch” rule to 6.18 inches, the mathematical ceiling is 6¼ inches; therefore, follow the specific pattern or worksheet rather than mixing its allowances with the basic chart. The example illustrates the important point: sashing changes the effective unit, and there is no single universal sashing shortcut.

Traditional cutting versus oversized-and-trim cutting

The chart gives traditional formula-based measurements. They use less fabric and are appropriate when your cutting and seam allowances are accurate. They leave less room for a slightly skewed block, bias movement, or trimming error.

An alternative is to cut the triangle parent squares intentionally larger—one documented Fat Quarter Shop method adds an extra ½ inch to both the side and corner parent-square measurements—and trim the sewn section to size. This can be helpful for beginners, unstable fabric, or layouts that need careful squaring.

Extra fabric is a deliberate trimming strategy, not a correction to the geometry. A larger piece is not automatically more accurate: it still has to be aligned and trimmed correctly.

Directional fabrics and bias handling

Directional prints need a separate layout check. Two triangles cut from the same diagonal may not show a one-way print in the same direction at every corner or side. Plan opposing cuts, use paper templates if necessary, and place the fabric face up or face down according to the print direction before cutting.

The bias edges belong inside the quilt, but they can still stretch during piecing. Use an accurate ¼-inch seam, avoid pulling the fabric through the machine, support the growing top, and handle the pieces as little as possible. Starch or sizing can be an optional stabilization technique if it is part of your normal process; it is not required by the formulas. String & Story’s on-point guidance discusses bias handling and stabilization.

Troubleshooting

My triangles are too small

First check that you used the finished block size. A 12½-inch unfinished block normally requires the 12-inch calculation. Also check that you used multiplication for side triangles, division for corner triangles, and rounded upward rather than to the nearest eighth. If sashing or cornerstones are present, recalculate using the effective finished layout unit.

The outside edge is stretchy

Inspect the grain direction. Side triangles should have their long straight-grain edge on the perimeter. Corner triangles should have both short straight-grain edges on the perimeter. If a side space was filled with a triangle cut once diagonally, the bias may be exposed at the edge.

Best Value

Quilting Rulers, 7 Piece Acrylic Ruler, Fabric Cutting Ruler (12.5"X12.5", 9.5"X9.5", 6"X6", 4.5"X4.5",12"x6.5",9"x3",12"x2"), Sewing & Quilting Templates

• This ruler was made from a durable premium quality acrylic plastic, thickness is about 1/9 inch, laser-cut for a cleaner edge that, for easier cutting of fabric layers.
• The kit also includes 50 non slip grip rings, these non slip grips can help you avoid slippage of the ruler and template when using the rotary cutter.
• Perfect set 7 pieces super package, which are 12.5 x 12.5 inches, 9.5 x 9.5 inches, 6 x 6 inches, 4.5 x 4.5 inches, 6.5 x12 inches, 3 x 9 inches, 5 x 30 cm for you to meet your tailoring needs in daily life.
• The 30-, 45-, 60-degree and numerous lines on the ruler can be used in conjunction with your cutting mat for more precise cuts.
• Avariety of sizes to meet your various needs, Ideal for many forms of crafts, including quilting, sewing, patch working, piecing, borders, weaving, etc.

$16.99

Buy on Amazon

My corners do not line up

Check that the corner triangle was cut from the correct parent-square size and centered on the row or block edge. It is normal for a corner triangle to extend beyond both ends before trimming. Check the assembled diagonal rows and match their seams rather than trying to align ordinary horizontal rows.

My directional print is upside down

Do not assume all corner triangles can be cut identically. Recheck the fabric direction on the layout and plan mirrored or opposing cuts where the print requires them. Directional fabric may require additional yardage.

My pattern uses sashing

Do not use the plain-block column without checking the layout. Measure the finished sashing and cornerstones, calculate the effective finished distance, and test one section. If the pattern supplies its own triangle measurements, use those unless you are deliberately redesigning the setting.

My finished block falls between chart sizes

Use the formula with the actual finished measurement. For triangle parent squares, round the final result upward to the next ⅛ inch. Do not choose the nearest chart row if that would make a piece smaller than the calculation.

I cut the wrong diagonal

For side spaces, the parent square must be cut on both diagonals. For corners, it must be cut on one diagonal. Separate replacement fabric before sewing if the grain direction is wrong; trying to rotate a miscut side triangle may put bias on the outside edge.

I have extra fabric at the points

Small extensions at triangle tips are expected and provide insurance for the seam. Align the required corner or center, sew the seam, press, and trim the excess when the quilt center is squared. Do not trim away the points before the pieces are positioned unless the pattern specifically instructs you to do so.

Cutting checklist

• ☐ I measured the block’s finished size.
• ☐ I accounted for finished sashing and cornerstones, if present.
• ☐ I selected the side, corner, or setting-square column correctly.
• ☐ I know how many side triangles and corner triangles the layout requires.
• ☐ I divided side-triangle quantity by four and rounded the number of parent squares up.
• ☐ I will cut side parent squares twice diagonally and corner parent squares once diagonally.
• ☐ I checked that the straight grain will form the outside edge.
• ☐ I checked directional prints before cutting.
• ☐ I decided whether to use the traditional size or an oversized-and-trim method.
• ☐ I will test the layout before cutting all the fabric.

Frequently Asked Questions

What size setting triangles do I need for a 12½-inch unfinished block?

A 12½-inch unfinished block normally finishes at 12 inches. For a plain on-point setting, cut 18¼-inch parent squares for the side triangles, 9⅜-inch parent squares for the corner triangles, and 12½-inch squares for any setting-square positions. Verify the finished size before using the chart.

Can I cut every setting triangle once on the diagonal?

No. Cut side-setting parent squares twice diagonally so the long straight-grain edge forms the quilt perimeter. Cut corner-setting parent squares once diagonally so their two short straight-grain edges form the corner perimeter.

How many side-setting parent squares should I cut?

Count the side-setting triangles required by your layout, divide by four, and round up to a whole parent square because one side parent square produces four triangles. The number depends on the arrangement of blocks, not on block size alone.

Should I use the chart if my quilt has sashing?

Not without checking the geometry. Use the finished block, sashing, and cornerstone dimensions to determine the effective finished distance in the on-point layout, then calculate the triangle sizes or follow the pattern’s own measurements.

The Bottom Line

The reliable sequence is: finished block size → correct formula → round up → correct diagonal cut → straight grain on the outside edge. Use multiplication and a twice-diagonally-cut parent square for side triangles, division and a once-diagonally-cut parent square for corner triangles, and add ½ inch for a whole setting square. Treat sashing, cornerstones, directional fabric, and oversized cutting as layout-specific decisions rather than automatic chart adjustments.

Quick Recap

Bestseller No. 1

Quilting Rulers,Sewing Ruler,4 Piece Acrylic Square Quilting Templates,Clear Precision Ruler for Quilting Sewing,Tools Supplies Accessories Green(3.5"x3.5" 5"x5" 6.5"x6.5" 10.5"x10.5")

$9.99

Bestseller No. 2

Sewing Ruler,5 Piece Quilting Rulers,3 x17 Inch,1.5 x17 Inch,3 x12 Inch,1.5 x10 Inch,1 x6 Inch,Acrylic Ruler,Cutting Ruler with Non-Slip Rings (Black and White)

$9.99

Bestseller No. 3

8 Quilting Rulers(3.5",5", 8",10",12.5",6.5"x12",2"x12",3"x9")

Quilting Rulers Non Slip:These Non-Slip Grips can prevent sliding during use

$18.78

Bestseller No. 4

Quilting Rulers Sewing Ruler,Acrylic Quilting Ruler Templates,Precision Cutting Tools for Patchwork Fabric,Sewing Supplies Purple(6"X17",3"X16",1.5"X12",1"X11")

$9.99

Bestseller No. 5

Quilting Rulers, 7 Piece Acrylic Ruler, Fabric Cutting Ruler (12.5"X12.5", 9.5"X9.5", 6"X6", 4.5"X4.5",12"x6.5",9"x3",12"x2"), Sewing & Quilting Templates

$16.99

ThatPainter Team

Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.