Tuesday, January 14, 2014

Disappearing Pinwheel math

Who knew that there would ever be an up-side to having a kid home sick with the flu.  He might be “grown” but it is a bit reassuring to know that I am not completely unnecessary as mother anymore.

It gave me a bit of time to work out the math for the Disappearing Pinwheel quilt.  I had seen the video from Missouri Star Quilt Co and thought it would be fun to work on so I was super excited when the Twitter buzz started about everyone working on that together for the MLK Day Sew In.

I wanted to try it using charm squares instead of a layer cake but had no idea what the finished size would turn out to be.  Since my son was super ill with the flu and couldn’t be left alone for the day I decided to dig out some scraps and work out the math while he was napping.

So here goes…

finished trial blocks


I had a candy bar (2 ½” squares) laying in the drawer so gave it a try, finished size = about 2” = Heck NO!, It was impossible to cut straight, the ruler kept wobbling because it was all seams and I couldn’t get it to lay flat no matter how much steam and starch I used. So I would only recommend that size for the super brave at heart or an experienced miniature quilter, obviously by the photo I am neither, it looks terrible.

Charm Square (5”), trimmed the pinwheel to 5 ¼” to make the math easier since quilting rulers don’t have 1/16” markings.  5 ¼” ÷ 6 = ⅞” so I cut ⅞” from the center on all 4 sides.  After piecing together into the churn dash block it was 4 ¼” so the finished size would be 3 ¾”.

I wanted to try it with the charm squares for a wedding quilt that I want to make for a May wedding.  I was already looking at a pattern that was churn dash and shoo fly blocks so this project was perfect.  But after realizing that I would need about 400 of them I decided to go with the layer cake size that was shown on the video.

Layer Cake (10”), trimmed the pinwheel to 12” to make the math easier.  12” ÷ 6 = 2” so I cut 2” from the center on all 4 sides.  After piecing together into the churn dash block it was 11” so the finished size would be 10 ½”.

Here is the EQ drawing of what I hope to accomplish with this.  Thinking reds and creams, maybe batiks...

red/cream disappearing pinwheels

Hope the math helps.


  1. Thanks for doing the math .... I was trying to figure it out but did not have time to do the sewing... I am thinking of using 12 in patches I already have from another project....I like the idea of even bigger blocks. ... looking forward to seeing all the pics of these blocks / quilts when everyone does them on MLK day.

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  3. Googling this quilt brought me here. Thank you for the math, but thank you for reminding me of one more thing before I tackle this project-that I can square up the pinwheel to a smaller size. Talk about an aha moment. Trimming the 12 inches just would make it even more easier, like that was possible!

    1. Apologies for the delayed response. So glad to have been a help. Would love to see photos when you finish.