Friday, May 11, 2012

Jelly Roll Quilt - The Math, Calculations

Let's start with step by step so I don't lose any one.  Let's call the top the head and the end the tail.
With a typical jelly roll, the strips are 2 1/2" - so they finish at 2"(we are going to talk in terms of finished size).  When you sew them all end to end, they are 2" x 1600".  When you bring the tail to the head and sew your first seam, your quilt is now 4" x 800".  Bring the tail to the head and sew again, now for the second seam, 8" X 400".  Are you seeing the pattern?  - 16" X 200", 32" x 100", 64" x 50".  If you would fold it in half again, it would be 128" X25".  I would say the most you would want to bring the head to the tail is 5 times (32 strips wide)- or to the 64" mark, because 128" is just too big!!

The question was asked about how many inches for queen size?  How many strips?
Let's aim for somewhere around 88" X 96" (mattress size listed as 60 X 80)

We are going to do this quilt as two Jelly Roll Race Quilts
Quilt 1
Let's start with Quilt 1.  We want this piece to measure 64" long X 88" wide.  Each Strip finished at 2", so that is 32 strips long.  So we need 88" Wide by 32 strips long (64")= 2816".  Converting that to strips would be 70.4 strips.  Remember - you are going 88" across with your strips.  If you are using full strips (around 40"), you are going to have basically 2 strips across in every row.  Don't forget to start with a half strip...or you could use half strip widths.
Quilt 2
We are now going to make quilt 2.  Since the first quilt was 64" long, we are going to make this one 32" long.  64+32=96".  So this quilt will measure 32" long X 88" wide.  Each strip finished at 2", so that is 16 strips long.  16 strips X 88 across = 1408".  Converting that to strips would be 35.2 strips.  Remember- you are bringing the head to the tail one less time on this quilt.

Sew Quilt one to Quilt 2 and square up.  Your quilt should measure approximately 88" x 96".

Back to the Math- and more ramblings by me......
  • My advice always Start with the length (32" or 64").  Remember...when you bring the head to the tail, one measurement doubles and the other measurement decreases by HALF.
  • If you want to make a baby jelly roll race quilt and you want to know how many strips (or inches) to use -If your length is 32", select a proportional width (around 28").  Using the formula 32" = 16 strips of 2" each; 28" wide X 16 strips = 448" (11 strips)
  • Lastly- don't be afraid to turn the quilt vertical!  64" can be your width.  Figure it the same way.  to make 64" wide X 80 long....32 strips X 80" Long= 2560" (or 64 strips)
  • You can make other lengths besides 32" and 64", but you will have to use your seam ripper.
If you made it all the way through this post, you probably think I am nuts for calculating this!  I hope this helps you on your adventure.  If you don't do the math, you may end up with something like this post.  Yes, I had to visit the seam ripper to make it proportional.  Don't be afraid to experiment with other size strips!  I wouldn't go less than 2" strips (1 1/2" finished).  What a great way to use up scraps.  The baby quilt I made was with 2 1/4" binding strips all different lengths that were left in a box.
Did I confuse you further or is it making sense? 

My Formula:
  1. Determine the length (32" or 64")
  2. Determine a proportional width to go with the length selected
  3. Take the # of strips (16=32" OR 32=64")multiplied by the Width desired (NUMBER YOU CHOSE IN #2) to get how many inches you need. 
  4. If you want to estimate strips, divide this number by 40.


Wendi said...

Thanks so much for making this easy to understand. I have been trying to do this myself and lose patience!!

Deb said...

Thanks for all of this info. I've been figuring out how many strips I need to make a I know to just sew two separate quilts together to make the size I need...duh!! LOL

Thanks again!

Anonymous said...

thank you for this great post and the explanations. i want to try my first jelly roll quilt soon, cutting my own fabric -- i was in desperate need for an explanation like yours! let's see how it turns out!

NCGrammyJean said...

I, too, thank you very much for all this calculating material. Math and I REALLY don't mix so you have answered a lot of my questions and provided direction.

I am going to give your link to the other quilters in my quilt group, many of whom are beginners. I know they too will appreciate you time and talent.
Thanks again. Jean

Zeromom said...

This is so great! Exactly what I was looking for. Thank you for posting this and in a way I understand. I'm so excited now!

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