Welcome to the third part of our Jelly Roll Race Quilt series. Be sure to read part 1, Jelly Roll Race Quilt :: Make a Quilt in an Hour?! and part 2, Jelly Roll Race Quilt :: Directions & Notes.
So your standard Jelly Roll Race Quilt makes a finished top that is approximately 50 x 60 inches. This is fine for a throw quilt, or if you add a border it would work for a full sized bed. But if you want to make a Jelly Roll Race Quilt for a twin, queen, or king sized bed, you need to do some math.
First of all, in order to change the size of the Jelly Roll Race Quilt, you have to understand how the quilt comes together. The width of the Jelly Roll Race Quilt is completely determined by the length of your initial mega strip. Assuming you would like a horizontally striped quilt, we can easily change the width by adding or subtracting the number of strips we add to our first mega strip. It is the length that gets a bit tricky.
Usually the fabric strips in a jelly roll are around 42 inches wide. We will assume some loss due to the selvedge edge and account for a 1/4" seam allowance on each side, so we will round each strip width to approximately 40". So 40 strips x 40" = a 1600" mega strip.
Now each time you fold the strip in half and sew up the side seam you loose half the width. So your width looks something like this...
mega strip 1600" wide
double row 800" wide
four layer row 400" wide
eight layer row 200" wide
sixteen layer row 100" wide
thirty-two layer row 50" wide
To figure out your quilt size you can work backwards from that. Let's say you want an 80" wide queen sized Jelly Roll Race Quilt and figure 80 (double it 5x), 160, 320, 640, 1280, 2560... so you need an initial mega strip that is 2560" long. Take your total mega strip length and divide it by the 40" jelly roll strip length and that will give you how many strips you need to sew together. 2560" mega strip / 40" jelly roll strip = 64 jelly roll strips needed.
Now, you may have noticed that we haven't changed the length at all. Using those 64 strips, your Jelly Roll Race Quilt will work out to be 80" wide by about 64" long. Now you could turn this Jelly Roll Race Quilt top sideways, so the strips run vertically and add a border (which is what I did with my "I Want Crazy" quilt) but if you want it to run horizontally and not a have a border we need to add length. For a queen sized quilt you probably want it to be more like 90-100" long.
In order to add this length, we actually have to make a separate piece. Why? Well, you have probably noticed the length pattern by now. Every time you fold your strip you double the number of rows of your Jelly Roll Race Quilt top. We can assume each row is 2" tall since the initial jelly roll strips are 2.5" inches tall with a 1/4 seam allowance on each side.
1 row = 2" tall
2 rows = 4" tall
4 rows = 8" tall
8 rows = 16" tall
16 rows = 32" tall
32 rows = 64" tall
Here is the problem... if we just fold it again and do another row like all the other rows we end up with Jelly Roll Race Quilt top that is 64 rows tall, approximately 128" tall, which is of course, way too big and would take a ton of fabric.
The solution is to add another section to the bottom of our original Jelly Roll Race Quilt top. Looking at the chart above, we can see that adding 16 rows will give us an additional 32" of length. So 64" + 32" gives us a reasonable queen sized quilt top of 96" long.
For this extra section we need to double our 80" width 4 times, not 5 like the original top piece... 80, 160, 320, 640, 1280. So we now need a second mega strip that is 1280" long / 40 strips = 32 jelly roll strips. Follow the same Jelly Roll Race Quilt directions for this add on section. After you complete this section, just add it to your original piece.
Your queen sized Jelly Roll Race Quilt, with horizontal strips, and no border, will take 64 strips for the initial quilt + 32 strips for the add-on section = 96 strips need for the whole Jelly Roll Race Quilt top. So you need 3 fabric jelly rolls (with 40 fabric strips in each jelly roll) to make this quilt.
A quicker formula to just figure out how many strips you need for your Jelly Roll Race Quilt is this...
(inches wide x number of rows) / 40" strip = number of strips needed
Lets try it... 80" wide x 48 rows = 3840 take that and divide by strip length 3840/40 = 96 strips... TADA!
You can now easily figure out how many strips you will need for any size Jelly Roll Race Quilt. Just remember, the length will be determined by the number of rows and that is a set number. Only the width is completely flexible. To add to your length you will have to make two separate pieces and combine them.
Here are the standard measurement for mattress sizes. Of course you will want your quilt to hang down a bit all around. But this will help you with your calculations.
Twin: 39 in × 75 in
Double/Full: 54 in × 75 in
Queen: 60 in × 80 in
King: 76 in × 80 in
Also, you can scale it down to make a super fast baby quilt with vertical strips. 42" x 32" (I like to keep my baby quilts sized to fit using 1 yard of fabric for the backing). So this would be 42" wide x 16 rows = 672. 672/40" = 17 strips. You could always cut your initial strips is half to give more variation on a little quilt. You will just need double the initial strips if they are half the length.
I hope that helps you figure out how to size your Jelly Roll Race Quilt to fit any size bed. Good luck and having fun sewing!