Friday, March 29, 2013

Math Tricks with Specialty Rulers!

I received an email from Vicki in Australia asking for some math help with figuring the sizes of strips she can use with the Easy Angle Ruler and Companion Angle Ruler while making the Lazy Sunday mystery that is currently running in Quiltmaker Magazine.

She writes:
Hi Bonnie
I have a question about Part 2. For the  4  1/4 inch squares what size would I cut them into triangles with using the ruler? I am having a mental blank. I have started doing the large completed units.

 We’ve all had those mental blanks before!
Before I go any further – this photo has NOTHING to do with the mystery currently running!  It’s just a photo from my archives of Quarter Square Triangles.  I wanted a photo that would be a grabber enough for you to stay and read this post ;c)
When working with specialty rulers like the Easy Angle and Companion Angle rulers, the first place you need to start is to find the FINISHED size of the unit you are making.  Sometimes a pattern with "regular rotary cutting directions" will list that, sometimes it won’t. Sometimes you can look at the finished size of the whole block and deduce what size each unit in the block should measure.
Because this is a mystery, and I haven’t received my issue yet, I’m not sure of how Quiltmaker has broken the steps down ---But with a bit of reverse algebra –let’s assume the following.
The magazine lists the cut square size as 4-1/4”.  If this is the unit I am thinking of – the finished size of the unit is 3”, so likely we are making quarter square triangles here.
Remember the math formula for Quarter Square Triangles?  Take the FINISHED size of the unit, and add 1-1/4” to give you the size of the square you need.  From here you proceed to cut that square with an X from corner to corner to give you four quarter-square triangles from each cut square.
EasyStreet 002
To use the companion angle ruler for these units, instead of cutting 4-1/4" squares, find the "FINISHED SIZE" of the quarter-square unit.  In this case I believe it is 3" (Again I don't have a copy of the magazine yet so I don't know how they broke the steps down)  Divide 3" in half = 1.5" (Because an hour glass unit is two triangles high!) Now add the seam allowance to that bringing it up to 2".  You will use a 2" strip and the companion angle ruler instead of cutting a 4 1/4" square with an X.
And it’s even easier than that – do you see those LARGE Numbers on the outsides of the Companion Angle Ruler?  Those are the finished “Hour Glass” sizes.  The numbers down the CENTER of the ruler tell you the size of strip to cut in order to get that size of finished unit.
It’s easier than you think to find out what sizes of strips you need --- but you need to start by finding the finished UNIT size before you can figure out the rest!
Something else to consider when finding what sizes of strips to cut for the quarter-square triangles in Flying Geese units:
The height of a flying goose unit is only HALF the height of an hour-glass unit….so if you know that your goose is going to finish at 2” X 4”  Add 1/2” to the 2” side to give you 2-1/2” and you’ll be cutting your goose triangles from a 2-1/2" strip.


Follow the large numbers on the outside of the ruler and take the FINISHED SIZE of the LONGEST EDGE of the flying goose unit --which will be 4".  ((It's 2" X 4" finished, right?))

Now  find the corresponding small number down the center -- see?? 2.5"! This way also tells you to cut 2.5" strips for flying geese units that finish at 2" X 4".
What about Half square Triangles?  How do you know which size of strip to cut for using the Easy Angle Ruler?
The “regular” rotary cutting method is to add 7/8” to the finished size of the unit to give you the size of strip or square you need to cut to get your unit to finish at the size you need.
Half square triangles that finish on the even INCH will have a measurement that says “Something + 7/8”.
Half square triangles that finish on the HALF INCH will have a measurement that says “Something + 3/8”.
There are two ways to figure out what size of strip to cut to use the Easy Angle Ruler.
Find the finished size of the unit and add 1/2”. (regular seam allowance) As in –the units finish at 2”, therefore I’m going to start with a 2-1/2” strip.
Take the cut measurement given, and subtract 3/8”.  That will tell you right off what size you are going to cut.  If the pattern calls for a 2- 7/8” strip – I know I can subtract 3/8” and have 2-4/8” which is 2-1/2”.
((Oh, I wish my 7th grade math teacher could see that I DID learn my fractions after all, but it took Quilting to make me understand it!))
This comes in handy when you need a unit that finishes on the half-inch in a quilt.  The pattern will tell you for a  half-square triangle unit that finishes at 1-1/2” to cut a 2-3/8” strip, cutting that strip into 2 3/8” squares. 
Subtract that 3/8” to use the Easy Angle – and you’ll be cutting your units from a 2” strip.
Easy Peasy, RIGHT?!
And do you know what that extra 3/8” is anyway?? Whether the measurement is 7/8” or 3/8” – that extra 3/8” is simply a DOG EAR.
You are going to remove that Dog Ear  before sewing your units into the quilt anyway – so why not remove them before you even sew and get more units out of less fabric in the long run using the Easy Angle and Companion Angle rulers!
No more Triangle Trouble – it’s all smooth stitching from here!


  1. Thank you for your clear explanation of how to use these rulers. I always get confused with the hour glass units--now that I understand how they work I shouldn't anymore!

  2. Anonymous8:00 AM EDT

    Thank you Bonnie. I have printed this out and will put it in the drawer with these rulers! I'm learning so much from your Blog.

    Linda Mc in IL

  3. Bonnie, I just checked my digital copy of the May/June issue of Quiltmaker. You are correct in your assumption that the 4.25" squares are used to make quarter square units.

  4. Bonnie, thanks so much for this very detailed tutorial! I am new to these rulers, bought them to work on my version of Easy Street, and they helped me get over my Fear of the Flying Geese, but I was flummoxed on how to use them in other projects...now I know just what to do! Thanks again!

  5. this is a great explanation! Are you going to put this with your tips and techniques? That would make it so easy to find later when I need it, lol

  6. Thank you thank you thankyou! I have to admit,I have these rulers and was not using them to their full potential! You took my"hmmmm" moment to an"aha" then "oh duh" appreciate the help!

  7. Step by step..Thanks so much..I will be printing this out also and keep with my rulers..as a matter of fact, I'll be making two copies..one for my rulers and one as a Master Copy to use when I lose the other one...

  8. Hi Bonnie! I am thankful for the math lesson. I am just cutting the fabric for step one and I do not see where QM listed finished sizes for the blocks, so I assumed that I cut the 2 7/8 square would be cut from a 2 1/2 strip using the Easy Angle tool, the 3 7/8 sq from a 3 1/2 strips. I learned a lot from Easy street. Thanks for all you do! :-)

  9. I was having the same problem, w a different quilt which is similar w the flying geese and a large center square. They were telling me in the pattern (and I'm a big pattern follower) to use 5.5" squares and 2&7/8 squares and sew them on the corners, cut in 1/2 and sew one on the coreners remaining.....not the easies, or simplist way to do it. I like the Easy angle way better.

  10. I strongly believe that quilting should be taught as part of the math curriculum. Don't you agree? It would make math make sense.
    I have always liked math but quilting actually gives it substance so you can see it in action. (Do I sound like a geek??)
    Love your stuff Bonnie. You join me for coffee every morning.

  11. Bonnie I just had to share...I have an Easy Angle ruler that I picked up on clearance at a Walmart, many many years ago. I have never used it but when I saw this post I thought, "hey this just may be the project to use this ruler finally"...when I pulled it off the pegboard still in the pkg...I had paid only TWENTY FIVE CENTS for it. Now how is that for a bargain.

  12. Thanks Bonnie, once again you make things so do-able.
    I don't know why these magazines don't embrace these rulers and directions

  13. Thank you for adding this to your Tips & Techniques tab. It's a great, precise tutorial.

  14. Thanks Bonnie, great information and you were certainly thoughtful to put this in your "tips" so I can easily find it.

  15. Thanks Bonnie. Can you make this a printer friendly page. I would like to print out without the ads so I can put it in my "Bonnie Binder"!

  16. the digital issue of quiltmaker I was able to get yesterday online!

  17. plus you have a web site "math of point" http://quiltville.com/onpointmath.shtml

  18. Thank you Bonnie. I too am going to print but my question, and the part I always screw up...when you say "finished" is that the size the unit (the hst or hourglass or goose) is when you've "finished" making it or the size it will be be after it's all sewn into the quilt?

    1. Could we have a printer-friendly link for this post please?

    2. There is already a Print Friendly icon just a little below Bonnie's signature. It's on the left hand side and is lime green. She's added that to all of her blogs.

  19. Anonymous3:07 PM EDT

    I loved the neutral post/tutorial you recently posted and then today's is so helpful too! Thank you for sharing and a big thank you for writing two wonderful detailed posts. They help us so much.


  20. Bonnie....you're awesome! And yeah, your Math teacher would be very proud of you! Who knew we would be using algebra and geometry on a daily basis, year later.....for FUN! LOL

  21. Thanks Bonnie for teaching us all about these specialty rulers. I use the Easy Angle ruler with almost every project I work on now. These instructions will make it easier for me use the Companion Angle Ruler more. You rock!!!

  22. Thanks so much.....you are simply the best

  23. Hi Bonnie, I saw another "quilting tool" in Home Depot - I was there with DH, walking all over the store finding the things he needed, as usual, when I spied a special display of Husky tools, which to me looked like a perfect set of tools for a longarmer! It is a telescoping magnetic tool (to pick up pins on floor, of course), a 4" magnetic bowl to hold the pins, and a swiveling mirror (to peek under the quilt to check the stitches underneath) It was only about $9-the telescoping tools are about $6 in quilt stores, so here we get all three! Wish I knew how to send a picture with this, but you get the idea! I got one for my own longarmer who is doing a special quilt for me right now! She was thrilled to get these tools, and I thought others would like them too. She said she'd have to hide them from the DH, tho!

  24. thanks for the great post on using these rulers. I use the nifty notions rulers that do the same job. I love it that you can cut more than one unit out of the same size strip. Can cut HST and squares from same strip.

  25. Hi Bonnie,

    This clears triangle rulers up nicely!
    Thanks so much. Also, the straight
    sashing/ cornerstone chart is

    Thanks again,
    Rebekah, KY

  26. Thank You Bonnie! I've been working on some LQS BOMs with 7/8" measurements. I was becoming frustrated trying to figure out the math (which I dislike), but you saved my bacon! I've got this one memorized, now.

    Thanks again - CHEERS from AZ


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