PM/GC Quilts Skill Builder Series: Part 9 – Diamond in Square

Welcome back for the latest Skill Builder Series post! Today I’m writing about the Diamond in Square component, which is also known as the Square in a Square. Be sure to check out Jeanne’s post over on Grey Cat Quilts about the Fifty-Four Forty or Fight block which features 60 degree triangles.

As with most of our posts, that are several different ways to create a DinS component. The traditional method isn’t difficult to sew, but determining the correct dimensions is a pain in the patoot. If you don’t know the necessary measurements (as in, you’re not working from a pattern) and want to skip the math, your best option is Method 2.

Method 1 – Traditional

The traditional method for creating a DinS consists of cutting a center square and two small squares that are cut once diagonally to create the outer triangles. Remember in the Flying Geese post where I talked about cutting squares diagonally once, in half, compared to cutting them diagonally twice, in quarters? Which you used depends on which edges will be exposed when the block is sewn together. The same is true here. If you cut a square in quarters and then sewed them to the center square, the bias edges would be on the outside of the unit. By cutting two squares in half, the bias edges are sewn to the square and the outer edges stay strong.

Before I get into the math, let’s just go through the assembly method. The center square must be cut to the correct size, but you can cut your outer triangles slightly larger and then trim. You still need to sew fairly accurate scant 1/4″ seams, but you don’t have to measure to 7/8″ and you can correct slight errors in sewing when you trim. Here I rounded up for the corner squares so I can show how to trim.

Note: If you want to cut to the exact measurements, you can try using a special ruler called Judy Martin’s Ultimate Point Trimmer. It helps you trim the points off before putting the triangles on the square, which in turn helps you align the pieces more accurately. I have it, and I’ve used it two or three times. I just have trouble remembering which way to line it up for the different kinds of triangles. Personally, I’d rather cut big and trim. (I know, I know – you’ve heard that a few times before!)

Cut a center 3 1/2″ square, and two 3 1/2″ squares of the outer fabric. Cut the outer squares in half once diagonally.

Fold the center square in half and press lightly to crease. Turn and fold the other way, pressing lightly again.

Place the first triangle right sides together with the square. Line up the edges and make sure the point of the triangle is on the crease you just created.

Sew using a scant 1/4″ seam. Press and repeat with the opposite triangle.

Repeat with the other two triangles, pressing and lining up with the edge and crease each time.

When you sew these sides on, the triangles form a point that indicates where your 1/4″ seam should be. The needle should line up in this notch.

Repeat with the last side.

Almost done! You can see that the block is larger than it should be – notice how the space from the point of the diamond to the edge of the block is larger than 1/4″?

Trim to exactly 1/4″ past the point on each side. Be careful to keep your ruler straight on the block when trimming or you’ll end up with a crooked block.

Note how the 1/4″ line matches up with the point on the left and on the top, and the horizontal line is the same distance below the point all the way across. You can also cut one side at a time, lining up a horizontal mark on the ruler with opposite points and trimming to 1/4″, then turning and repeating on each side.

Repeat so all four sides have been trimmed.

And there’s your Diamond in a Square!

Traditionally pieced DinS units require annoyingly fiddly math. For those who’d rather skip all of the math bits, here’s a chart. The Finished Block column is the size it will be when sewn into the quilt. The Center and Corner Square measurements are the sizes you CUT the squares. These numbers are rounded to the nearest 1/8″.

Finished Block Center Square Corner Squares
3 2 5/8 2 3/8
3 1/2 3 2 5/8
4 3 3/8 2 7/8
4 1/2 3 5/8 3 1/8
5 4 3 3/8
5 1/2 4 3/8 3 5/8
6 4 3/4 3 7/8
6 1/2 5 1/8 4 1/8
7 5 1/2 4 3/8
7 1/2 5 3/4 4 5/8
8 6 1/8 4 7/8
8 1/2 6 1/2 5 1/8
9 6 7/8 5 3/8
9 1/2 7 1/4 5 5/8
10 7 5/8 5 7/8
10 1/2 7 7/8 6 1/8
11 8 1/4 6 3/8
11 1/2 8 5/8 6 5/8
12 9 6 7/8

Now for the math! (If you’re not interested, just skip to Method 2. I promise, it’s much easier!)

Here’s the formula when you know the size of the center square and need to calculate the corner squares:

Center square / 1.414, rounded up to the nearest 1/8 inch, + 7/8 inch (.875) = size of the outer squares.
For example, let’s say the center square is 3 1/2″.
3.5 / 1.414 = 2.475 rounded up to 2.5 + .875 = 3.375 (or 3 3/8″)

Blech. Unfortunately, there’s no easy way to get around this. Believe me, I tried. That’s why this post has taken so long! The best suggestion I have if you’re going to use this method is to round up for the corner squares. In this example above, I rounded up to 3 1/2″. (Don’t let the fact that the center square and outer squares are the same size trick you into thinking this is always the case. For a 9″ center square you need 6 7/8″ outer squares.) This calculation also comes in handy when you’re cutting setting triangles.

Here’s the next problem: the math is backward. It tells you how to cut the triangles when you know the size of your center square. But most blocks are created at a specific size, so you need to know the measurements from the block in, not the center out.  If you knew the size of the center square, you’d be able to calculate the outer squares for cutting the triangles. But how do you figure that? Well, it’s that same “magic” number: 1.414.  This time the math is even more fiddly.  First, you need to start with the “finished” sizes of the pieces. For example, say you want to make a DinS that finishes at 12″. That means the block will be 12 1/2″ before you sew it into a quilt. Next, divide that finished size (12″) by 2. This gives you the finished length of the short sides of the triangles (in this case, 6″.) Next, you MULTIPLY by the magic number, 1.414. This tells you the approximate length of the long side of the triangles, which is the same as the measurement of the center square. In this case, that would be 8.484. That’s the finished size, so you need to add 1/2″ seam allowance for a total of 8.984. Round to 9″.  Here’s the short version of how to calculate the size of the center square:

Finished block size / 2 x 1.414  = Finished center square + .5 = Cut center square

Got all that? Good. Let’s move on to something easier.

Method 2 – Squares

This is the simplest method for creating the DinS component. You use only squares, so there’s no bias edge to worry about, and the measurements are pretty easy to calculate. It’s greatest drawback is that it wastes some fabric, but, as with the Flying Geese unit, you have the option of sewing a second seam and saving the HSTs created with the waste.

Measurements are based on your finished block size (not including seam allowances). Start with your center fabric. Cut a square that is 1/2″ larger than your finished block size. For example, if your finished block will be 6″, cut the center square at 6 1/2″.

Next cut four squares for the corners. The squares should measure half the finished block size plus 1/2″. So if you finished block is 6″, your squares should be cut at 3 1/2″ (half of 6 is 3, plus 1/2″ is 3 1/2″).

Draw a diagonal line from corner to corner on the wrong side of each of the small squares. If you use a seam guide on you machine, you may not need to draw the lines – just line up the point with the needle line and sew, keeping the point on the seam guide line.

If you want to reclaim your waste fabric, sew a second line 1/2″ outside first line. (Draw this line, too.) With smaller blocks you often don’t have enough excess fabric in the corners to create HSTs. Sew the squares onto opposite corners first.

Trim the excess fabric, saving the HSTs if you sewed the second seam.

Press the triangles (pressing to the side or open makes little different when assembling these into blocks, so do whichever you prefer). Sew the next two squares in the same manner.

Trim the corners off, again saving the HSTs if you sewed the extra seams.

Press, and you have a Diamond in a Square!

As you can see, this method is great for special fabrics that you want to fussy cut, since the square doesn’t get turned on its point the way the first method does. You can fussy cut the other way, too, but this way is a little easier.

Method 3 – Square in a Square Ruler

If there’s a popular component in quilting, you can bet there’s a specialty ruler created to go with it – in this case it’s the Square in a Square Ruler by Jodi Barrows. As with most specialty rulers the additional cost of the ruler should be considered. This one is on the expensive side because it includes a book. I have the larger original ruler, but the “mini” ruler works the same way. There are certainly benefits – you work with squares and rectangles, never triangles, and you trim after sewing so it’s more accurate. It can be used to create other components such as HSTs and Flying Geese. However, there are also some drawbacks. There is unavoidable fabric waste, and unlike the squares method above, there is no way to recover the waste. It’s just scraps, usually too small to reuse. You end up with exposed bias edges that are prone to stretching. Finally, fiddly math is required to determine the size to cut the rectangles. Bottom line: It works, it’s a fun tool, but if you are able to create the component without it, do so. Since it’s a fairly specific ruler and most of you don’t have it, I haven’t included instructions on how to use it. If you’re interested, leave a comment. If there are enough people interested, I’ll demonstrate it in another post.

Method 4 – Foundation Piecing

I’m not going to go into great detail about this method because we haven’t covered foundation piecing (also called paper piecing) yet. Those posts are still down the road a ways, but if you are already familiar with foundation piecing, you can easily draw DinS foundations. The greatest advantage to foundation piecing this component is THERE IS NO MATH! Well, essentially no math. You need to know the finished size of the component, then draw it accordingly. But that’s just finding the halfway point on each side – folding the paper works as well as anything.

Using the DinS Components

The DinS component is different from many other block components in that you can keep adding to it as long as you can find fabric wide enough to create the triangles. Here it is with additional rounds of triangles.

A block with two rounds of triangles is called the Economy Patch, and is also used in the Storm at Sea block.

If you start with a four patch for your center square and continue adding rounds, you create the Monkey Wrench or Snails Trail block. Color placement is important to create the spiral effect.

Since you can create a Diamond in Square in any size, you can use a DinS as the center of a block…

…or even use pieced blocks as the center “square” and build one or more squares around them.

Whew! When I started this post I was going to make samples of the Snails Trail and Economy Patch, but I think I’m just going to post it with EQ7 illustrations. I’d like to post it before my next birthday!

Does anyone have any questions, or any suggestions for making the Diamond in Square component?



  1. Very informative (as usual).

    Please keep this series available for a long, long time – I will need to refer to it as I progress through my quilting experiences!

  2. This was so helpful. Thank you. I have been working the math whenever I have wanted to make these. Your chart is wonderful. I am really enjoying these skill builder posts.

  3. I have just discovered your blog, and it is fascinating! Thank you for the copyright post, Great stuff! And I love the free basket blocks on the side. I think i have all of them in the various books on blocks that I have in my library but seeing them all in one place has given me some ideas. I followed a link from over here and am so glad I did.

  4. I have been loving your skill builder series for a very long time now and I have even reread them throughout the last six months a few times but I have never taken time to Thank you for all of your hard work and especially all the time you have spent posting them. I don’t think a published book is better and you need to know that there are people who don’t have blogs but love to read yours!

  5. thank you so much! i was struggling on another tutorial…couldn’t get the center block big enough for some reason. thought i was doing something wrong, but looks like it was just a measurement mistake in their directions perhaps? anywho, i used your chart and it turned out perfectly! i will be adding a link to this page once i write up my blog post so more people can use your help. very happy right now, because i was seriously getting discouraged!

  6. OK, I’ve been trying to make my cornerstone all afternoon guessing at how to get a 2 1/2″ cornerstone. Finally I decided to try the internet and came across your instructions! Thank you so much. Everything was so clear. On the first try using method 2 I did it!! Since I need to fussy cut that’s the best method for me.

  7. Your terrific site shares many useful sewing/patchwork info and it’s Truly Wonderful! I’ve never seen so many different ways to do DinS or Sq in a Sq. blocks. They’d be great for making cornerstones. I just have one question – and qonder if you know the answer… How can I make a chain of these blocks without having to sew each (separate) block together, one at a time? Surely someone’s come up with a (shortcut) way to make a chain of them. I’m trying to make a wide border using DinS blocks (either in a long connecting chain) or separated by blank square blocks going all around the border. PLEASE tell me if anyone knows how!!! thanks,

  8. Thank you! It is so helpful to have several methods brought together and pros and cons and best applications of each technique compared and discussed. I have been going around in circles with some of these seemingly simple ideas! I will be studying your series closely!

  9. I’ve been making a few diamond in a square units lately but I’m not too happy with them. I use method two and my problem is which way to press the seam when I connect it up to the other units in the block. You can’t pinwheel the seam allowance. The points act all lumpy…. Flipping them all out is not always an option…. sigh. Anyone got any pointers on making the whole thing lie flat when it’s in the middle of a bigger block? Thanks!

Comments are closed.