Square in a Square Tutorial & Top Tips

March 2023 Update: I now recommend cutting the smaller squares ⅛” larger than listed in the table (so 1½”, 1¾”, 2″, 2¼” 2½”, 2¾”, 3″, 3¼” 3½”, … all the way up to 7″) and using a FULL ¼” seam when sewing the triangles on the side of the large square. I have found a lot more consistently in my piecing of square in a square blocks with this update.

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Last month I shared a tutorial and my top tips for making no-waste flying geese. Another block that I’ve worked with over the years that is surprisingly tricky is the square in a square block, so today I’m sharing a tutorial and my top tips in case anything I have learned is helpful. As always, if you have a tip that works really well for you when you piece square in a square blocks, be sure to share it in the comments!

Square in a Square Table and Basic Instructions

Square in a Square Table and Illustration

When making square in a square blocks, I prefer to work with the block sizes listed in the table above. If, after using all the tips that I share in this post, you are still struggling with square in a square blocks that are ending up too small, you can cut the smaller squares ⅛” larger than listed in the table. However, I’m confident that like me, once you give these tips a try you’ll find that you are making square in a square blocks that need minimal trimming!

1. Cut (2) small squares in half from corner to corner to create (4) triangles.
2. Using a ¼” seam allowance*, center** and sew (1) triangle to a large/center square. Center** and sew a second triangle to the opposite side of the large/center square.
3. Press to set seams and press seams open. Trim dog ears.
4. Using a ¼” seam allowance*, center** and sew the remaining (2) triangles to the remaining sides of the large/center square.
5. Press to set seams and then press seams open.
6. Trim to the unfinished size as necessary, removing dog ears and making sure there is ¼” between each point of the center square and edge of the trimmed block.

*See Tip #1
**See Tip #5

For the purposes of this tutorial, I will be making a 4″ finished (4½” unfinished) block using a 3⅜” center square and 2⅞” small squares.

Tip #1 – Sew a Test Block (or Two!)

My absolute best tip for square in a square blocks is to sew a test block to establish the correct seam allowance for the size you are making: depending on the size block you are making, you will need to vary between a scant ¼” and a true ¼” seam allowance in order to get the block to trim correctly, leaving ¼” beyond each point of the center square.

Take a look at the values of the squares in the table: the small squares vary in a consistent manner with an increase of ¼” for each increase in block size. Note that the center (large) square size does not vary consistently at all. Therefore, each block size will require you to find the “sweet spot” of seam allowance. I’ll discuss this more as we work through piecing a sample block and the other tips.

Tip #2 – Cut Using Rulers

Cut Using Rulers

For years, I cut everything following the grid on my rotary cutting mats, but once I committed to changing how I cut my fabric and instead cut using my rulers, I saw a huge improvement in my piecing accuracy (see more photos for how to cut using rulers in the No-Waste Flying Geese Tutorial). When cutting a square with my ruler, I like to make sure that the 45-degree angle of my acrylic ruler falls right at the lower left-hand corner prior to my final cut (note that I am right-handed; left-handed quilters will rotate the strip 180-degrees, rotate the ruler counter-clockwise 90-degrees, and line up the 45-degree angle in the lower right-hand corner prior to cutting).

Top Tip #3 – Nudge Ruler When Cutting Squares Diagonally

Nudge Ruler When Cutting Squares Diagonally

Rotary Cutters are thin, but they do have thickness. I like to align my ruler’s 45-degree line with one edge of the square and slide the ruler down 1-2 threads to account for the thickness of the blade.

Nudge Ruler When Cutting Squares Diagonally – Detail

The above detail photo is a bit exaggerated to demonstrate; I would set the ruler to be about half of this shown offset prior to cutting. The combination of lining up the edge of the square with the 45-degree line on the ruler and this small offset help the diagonal cuts be precise and the two triangles as even as possible.

Tip #4 – Handle Triangles Carefully

Note that once the squares are cut on the diagonal, the diagonal edges of the triangles are bias edges. Bias edges are more prone to stretching, so handle the triangles carefully and as little as possible. Ideally, I aim to cut the squares and piece with them the same day. This is not always practical, but it’s something I do keep in mind.

Tip #5 – Fold Center Square in Half

Fold Center Square in Half

Fold the center square in half both directions and gently finger press or lightly set with a warm iron to create reference lines.

Center Triangle on Reference Line

When aligning the side triangles, place the tip of the triangle along the reference line made when folding the center square in half.

Note that I do not recommend marking the seam allowance on the triangles and that the line in the above photo is for demonstration purposes only. Because the long edge of the triangle that will be sewn is the bias edge, marking a reference line after the triangle is cut could easily distort the edge of the fabric, so I do not recommend doing this unless you press lightly and take care not to distort the bias edge.

Tip #6 – Sew Consistent Seams on All 4 Sides and Measure Seam Allowance

Measure Seam Allowance

When in doubt, I always start with a scant ¼” seam allowance. After sewing your seam allowance, measure prior to pressing your seams to check for consistency of your sewn seams and to understand the setting you are using. In the photo above, you can see that I did sew a scant ¼” seam allowance (1-2 threads less than a full ¼”).

Tip #7 – Trim Dog Ears with Ruler (First Two Triangles)

Trim Dog Ears with Ruler

When trimming the dog ears after pressing the first two seams open, I align the block under my ruler. I’m looking to make sure that the center square is aligned with the expected width (3⅜” in this case) and that the two sewn seams are horizonal and aligned with marks on my ruler prior to trimming the dog ears.

Tip #8 – Trim Dog Ears with Quick Freehand Trim (Last Two Triangles)

Quick Freehand Dog Ear Trim

Prior to pressing the last two seams open, a quick freehand trim following the straight edge of the underlaying triangle edge removes the dog ears quickly and easily.

Tip #9 – Final Trim and Evaluation

Final Trim and Evaluation

After sewing your test block, it’s time for the final trim. Remember the crease marks on the center square? They are perfect for lining up with your ruler’s 45-degree line!

The things I am evaluating when I trim down my square in a square blocks are:

• Do the points of the center square fall at the halfway point on all 4 sides (2¼” in this case)?
• Do the points of the center square fall ¼” away from the trimmed edge?

Tip #10 – How to Adjust

If the points of the center square are LESS than ¼” away from the edge of the trimmed block, then sewing with a larger seam allowance will help adjust them into the correct position.

If the points of the center square are MORE than ¼” away from the edge of the trimmed block, then sewing with a more scant seam allowance will help adjust them into the correct position.

Note that because I sew my blocks together with a scant ¼” seam allowance, I am okay if the points fall one or two threads less than a full ¼” from the edge of the trimmed block. In the case of the block I am showing under Tip #9, I would be happier if I sewed with a true ¼” seam allowance instead of the scant ¼” seam allowance for this sized square in a square block.

Feel free to pin the image above so that you can come back and reference these tips the next time you need to make square in a square blocks.

Are there any other quilt blocks that you would love to see me cover in an in depth tutorial and tips post like this? Let me know in the comments!

Linking up with Tips and Tutorials on the 22nd with Kathleen McMusing.