Thursday, 13 March 2014

Decipher Your Quilt: 2-Patch Blocks

It's that quilt deciphering time of the week again! I wanted to mention quickly that I have updated my post from last week in response to a few (no-reply blogger) questions left in the comments. Lots of you were interested in the non-slip stickers I use on my rulers, so I've added a photo of those, and gone into a bit more depth in some of the cutting information.

Today Leanne who blogs at She Can Quilt and I will both be talking about 2-patch blocks and some of the calculations you might encounter when working with these blocks. 2-patch quilt blocks are something you've probably made a thousand times - the humble half-square triangle (HST) block is a perfect example of a 2-patch. You will often find 2-patch units as part of more complex blocks, but they do stand alone as a block by themselves as well. The 2 patch blocks you will encounter most often are HSTs and square blocks made from two rectangles, so I will be talking specifically about the calculations pertaining to these blocks. There are a few other examples of 2 patch blocks, such as the Drunkards Path block, but Leanne will cover those in detail later in the series when we cover circles.

Although 2 patch blocks are simple to construct, they can both produce some pretty spectacular quilts. This first quilt was designed by Amanda Jean of Crazy Mom Quilts (free tutorial here), and it is completely constructed from rectangle-based blocks. This is a very clever way of creating a zig zag design without sewing any bias edges, and almost identical in design to one of the HST quilts in the mosaic below.

HSTs are found everywhere in quilting; there are some amazing quilts out there constructed entirely from these 2-patchs, but they are also a very important unit in countless other quilt blocks. When it comes to quilts made from HSTs, you only need search for HST quilts on Flickr to see the huge variety of quilts you can make from this block. The quilts in this mosaic are all HST quilts, and it hopefully gives you an idea of the type of quilts that are possible with HSTs.

1. HST quilt 3, 2. HST quilt layout, 3. HST Parisville Quilt - Le Mille, 4. Hullabaloo HST quilt, 5. Hst Quilt, 6. Daniel's quilt, 7. HST Warm Cool Quilt, 8. HST quilt top, 9. HST trip


Because you'll encounter them so often, it's useful to understand how to calculate what fabric you will need to make a given size HST. There are several methods for making HSTs, so I will talk through each of them and their calculations. First up though, there are a couple of points that relate to each of these methods
  •  I ALWAYS make my HSTs a bit bigger (about 1/8" or 1/4") than I need and then trim them down to size, so that my points are good. I do this regardless of the method I am using to make the HSTs, so all my calculations here will include this margin for error. I'm not sure if it's just me, but if I don't trim my HSTs my points end up pretty awful. 
  •  I press my seams open for HSTs, as I find it much easier to match my points and to end up with a flat block. 
  •  For each of these methods, I will be making 2" finished (2.5" unfinished) HSTs, but I will mention how to work out what sized squares to start with for other sized HSTs.

1. Traditional Method

This method involves cutting squares of fabric, then cutting the squares diagonally and sewing along the resulting bias edge. These squares should be 7/8" bigger than your required FINISHED size block - but I round this up to 1" bigger, since it gives a bit more wriggle room if you're not spot on with your seam. There is also something nice about cutting whole numbers, rather than teeny fractions :o)

For example, to make a 2" finished HST block, I would start with two 3" squares (one print, one background) and cut them diagonally...

... and then sew them together along the bias edge, and press the seam open ready to trim it to size. How you trim HSTs is critical - in the photo below you can see I have lined up the seam along the 45 degree line on my ruler. This needs to be lined up in order for your points to be accurate once the HST block is sewn together with other pieces. The other important thing to check here is that you have left sufficient fabric on the bottom and left hand sides to trim these sides as well. You can see here my 2.5" markings are sitting well over the fabric (in fact, I could move the ruler down and across to leave more fabric at the top of the block), so I will be able to do this. Trim the right hand side and top at this stage.

Next, turn your HST so that the squared edges are lying under your ruler, with the sides aligned with the markings on your ruler (in this case 2.5"), and that the 45 degree line is still lined up with the centre seam. You can now trim the remaining two sides as per step one.

I don't tend to use this method, as I avoid sewing raw bias edges whenever I can. It does give good results though, and the edges of the block follow the grain of the fabric, so when  multiple HSTs are sewn together you don't need to worry about bias edges.

2. HSTs 2 at a time 

This method involves cutting squares of fabric, marking the lighter fabric along the diagonal and sewing 1/4" away from the line on both sides. Again, the starting squares should be 7/8" bigger than your required FINISHED size block - but again, I round this up to 1" bigger.

For example, to make a 2" finished HST block, I would start with two 3" squares (one print, one background), and mark the diagonal on the wrong side of the lighter fabric. I just use a pencil or a normal ball point pen for marking these lines.

Sew along both sides of this line, using a scant 1/4" seam, and then cut along the marked line.

Press the seams open, and trim the HST as per the method above.

This method is normally my preferred method for a few reasons. I like that the edges of the block are on the grain, and that you produce two HSTs at a time. I realise some of the other methods yield more HSTs, but I tend to use a large variety of prints in my quilts, so two the same normally works better than four or eight. I also like that I can chain piece a bunch of these squares at a time.

3. HSTs 4 at a time

This method involves starting with 2 larger squares of fabric, sewing around the four edges and then cutting along both diagonals to produce four HSTs.

To figure out the size square you will need to start with for this method, you can use this little formula (which includes room to trim the HSTs down to size):

Starting Square Size = Unfinished HST Size / 0.6

So for this example, I want to make 2.5" unfinished HSTs.

Starting Square Size = 2.5/0.6 = 4.17

If you are left with a tricky number like this, ROUND UP to the nearest 1/4". So I would round 4.17 up to 4.25. I would be hesitant to round down, just in case it left you with too little fabric to trim them.

For example, to make a 2" finished HST block, I would start with two 4.25" squares (one print, one background).

To make HSTs using this method, place your two starting squares right sides together, and sew around all four edges. Cut the square along both diagonals, to produce four HST blocks, and trim down to size using the same method as before.

I must admit I really don't like this method. It is good in that you produce four HSTs at a time, but the edges of your block will all be bias edges (not something I like). I also find it quite difficult to sew around the edges of the squares accurately - I seem to get a lot of shifting as I sew and occasionally get puckers. But, a lot of people love this method, so if you've never tried it you might find you love it!

4. HSTs 8 at a Time

I first came across this method for HSTs after reading Lindsey's post on Sew Mama Sew. It is a great, fast way to produce a lot of HSTs. This method involves marking both diagonals, sewing 1/4" away from both lines and then cutting vertically, horizontally and along both diagonals. It is very similar to the HSTs 2 at a time method, but produces 8 HST blocks.

To figure out the size of your starting squares, you can use this formula:

Starting Square Size = (Finished HST size + 1) x 2

It is important to calculate the part inside the brackets first, and then multiply by 2. For example, I will be making 2.5" unfinished HSTs, so

Starting Square Size = (2 + 1) x 2 = 3 x 2 = 6"

So to produce eight 2" finished (2.5" unfinished) HSTs, I would start with two 6" squares of fabric (one print, one background), and mark both diagonals on the wrong side of the lighter fabric and then sew 1/4" away from both sides of both of these lines.

Once these are sewn, mark both the vertical and horizontal lines that run through the centre of the block, and cut along all four of these marked lines. Press your seams and trim as per the method shown above. 

There are also paper templates (thangles) and specialty rulers available that are designed to make HST block construction easier. Although I haven't personally used any tools like this, I have heard great things about thangles and bloc loc rulers in particular.


The maths involved in making rectangle based blocks is fairly straight forward. The critical point to remember is that when doing quilt block calculations, you need to remember that you will lose 1/4" on each side of each piece of fabric when they are sewn together. So if you're starting with a 5" square, you will lose 1/4" off all four sides and it will end up 4.5" square once it is sewn into a block. Whenever you are calculating fabric sizes for any block, you will need to add 1/2" to all finished measurements to account for your seam allowances.

So to make a 6" finished block (6.5" unfinished) composed of two equal rectangles:

The long side of each rectangle will be the finished measurement plus 1/2" - so in this case 6 + 1/2" = 6.5".

The short side of each rectangle will be the finished measurement divided by 2, plus 1/2". ie 6/2 + 1/2" = 3.5".

I will send you over to Leanne's excellent post on rectangle blocks, and some of the patterns you can create using these simple blocks.


I first tried to make these blocks back when Jess and I ran our sampler QAL, and they caused no end of headaches. In the end, the only way I could figure out how to make them so that my points were okay was to draw up paper templates and paper piece them.

For example, for a 6" x 3" finished half-rectangle triangle block, I would draw a 6" x 3" rectangle on paper, and mark the diagonal. This does NOT include seam allowance, so I would cut my template 1/4" away from each edge when trimming. I would love to hear if anyone has an easier way to make these and still get the points to line up :o)

If you would like to practice some of these HST methods and still make something lovely, Leanne has written a fabulous tutorial for a tote bag that uses HSTs. You could also choose one of the many HST based blocks Jess and I wrote tutorials for for our QAL - this would be a good opportunity to practice re-sizing HST blocks. If you do make anything using our tutorials this week, please add it to the Flickr group or use the #decipheryourquilt hashtag on Instagram.

xx Jess


Leanne said...

We do think alike on this one. I am going to make another zig zag quilt, preparing for this post has inspired me.

Rosa said...

Thanks,thanks for these tips!

Your quilts are fabulous and also your fabrics combo.

Katy Cameron said...

Ahh, so many ways to create little triangular nightmares ;o)

Patti said...

I was really curious about the method for cutting half rectangles too. Luckily, I love paper piecing, but wouldn't want to do a kazillion of them! Great series you are doing ladies. I can always use a refresher for cutting hst's.

Anne said...

Thanks for putting this all together in one place. I'm like you and always make my HSTs oversize.

Leslie Frost said...

I was thrilled recently to learn that you can trim up HSTs before you open and press them, and now I love this method. Have you tried that?

Benta AtSLIKstitches said...

Thank you Jess, interesting, informative AND inspirational! Well done! Time to make another zigzag quilt!

(I was given some iron on interfacing with sewing and cutting lines to create loads of HSTs, I'm not a fan of them, but it did make decent blocks when I tried it)

Newbie Jen said...

brilliant, as always