Figure how big to make corner & setting triangles using the QuiltSandwich Triangle Calculators — PLUS — tips on how to cut big squares for large setting triangles

To the left is a picture of the quilt I am working on now. I have been trying to clear out some unfinished projects this summer.

​The quilt will eventually be set on point and I have all of the blocks and rows assembled and came to the part where I needed to cut the setting triangles. The blocks are big- the ones in the picture measure 14 1/2" with the sashing.  That's a BIG setting triangle. The pattern called for 20 1/2" squares. For many years I struggled with cutting big squares until I discovered how to do it.  ​

I learned from Anita Grossman Solomon, I think it was on The Quilt Show that the way to cut a large block was to fold the fabric and then cut a smaller square.  But if you have to cut them on the diagonal into quarter square triangles that's tricky too because the diagonal is so long.

So here is how I did it.

First, rough cut out the length of fabric that is needed.  In my situation, I needed to end up with a 20 1/2" square.  So I cut my fabric at 22".  At this point I have not squared it up or anything.  Tearing the fabric would be good too because it would give you another grainline to work with.

As a side note- do you like my animal stickers?  My granddaughter Ariel decorated my cutting table for me.  She was 2 at the time.  Good job don't you think? ​

Next:  I squared off the end on the left hand side and then folded the fabric in half.  All of the rough cut edges are on the top and the right hand side square. 

Here is where the magic comes in.  For a 20 1/2" square  cut on the raw edges ( not the sides with the folds or you will be very sad) a square that is 10 1/4".  How did I get that number?  Half of 20 1/2" is 10 1/4"  (20.5 divided by 2 equals 10.25 or 10 1/4".  Here's another example:  If you needed a square that was 32" then you would fold your fabric as shown and cut a 16" square.   A 33" square would be 16 1/2" 


Isn't that easy?


So here goes: I used my 15 1/2" square ruler to make these cuts.  I lined up squared up edge to the 10 1/4" line on my ruler.  And then made my cuts.  Remember!  Don't cut the sides that have the folds, only raw edges.  ​

Both sides were squared up to 10 1/4". Here is my 20 1/2" square!

Ok now we're cookin' with gas!  All that is left is to cut that big square into quarter triangles. I cut my triangles from the unfolded square and because the fold lines left a mark, I can use the center of the square where the horizontal and vertical lines intersect to my advantage.​

I know its kind of tough to see, but if you look close you will see the fold lines. I then took my 24" ruler and lined it up in the corner and made sure I was in the middle of the square and used a pencil to draw a line. Then I moved my ruler down to the other corner and did the same thing. Because I was only drawing a line form the corner to the middle, I didn't need to have a super long ruler.  Upon thinking about it one could have folded the square on the diagonal too to "mark" the cutting lines. But I think drawing the line would be just a bit more precise. Draw the lines for both diagonals.

I know its kind of hard to see the pencil lines — I should have used a marker — but I was taking the pictures using the fabric for this quilt and I didn't want to not have enough in the event I made a mistake! ​

I then cut the triangles out one at a time.  I don't try to go from corner to corner. The ruler isn't long enough and it would be hard to keep it from slipping. But just cutting from the corner to the middle on the pencil line is a comfortable distance to cut. 

Voila!  4 quarter square triangles from a 20 1/2" square!

Now- just for grins- let's say that I was working from my own quilt design and I needed to figure out how big to make my corner and setting triangles. How would I do it?  I would just use  the QuiltSandwich triangle calculators. The triangle calculators are found under Notions. Select the kind of triangle you want to cut, and simply input the finished size of the block you are working with and the cut size will magically appear. Need to cut several? Input the size and number of the squares needed into the Yardage Calculator to get the amount of fabric needed. Be sure to check your allowances to allow for the rough cuts! 


Now that's the kind of math I can sew with!


Here's to joyful quilting!