Rectangles, leftovers, & quilt math

When I was piecing the Dutch Windmill top I had a strip leftover from each fat quarter just wide enough to use with the rectangle die in my 8 inch Qube. I mentioned the other day, I like to save myself work so I cut a stack of rectangles and set them aside for later. In fact I set them aside for 4 months and couldn’t remember at first what quilt they were leftover from when I started sewing them together. 

I love using rectangles in quilts … the two most recent ones are still waiting for quilting….both of them RWB and intended for veterans when they’re quilted and both were based on antique quilts I saw on eBay. 

Here’s a little Windmill one made from a set of 2.5 inch batik strips that is actually finished. 

All 4 quilts were made without patterns which is where the quilt math comes in. The two most frequent requests I get on my website are to resize the quilts and to list fabric amounts, usually in the size quilt they want to make. Needless to say, I don’t provide those services and usually tell them they’ll have to calculate those things for themselves. I’m just too busy with my own quilting!!

Most experienced quilters know the easiest way to resize a quilt are to add more blocks and/or borders. In the case of Becky’s king size quilt, the quilt pattern I wanted to use was throw size and I originally planned to add more blocks and use the yellow border fabric to bring the quilt up to a size to fit her bed. After getting a number of blocks on the design wall, we decided the border fabric wasn’t working and therefore I needed more blocks. So I redid my math …

I use Notes on my iPad to write down my calculations so I can refer back to them as needed. It’s just that easy …start with the size of the quilt wanted, determine size of the block, and divide the block size into the length and width to get the number of blocks needed across and down … multiply those two numbers to determine the total number of blocks needed. 

Borders allow you even more flexibility to inch up to the size quilt you want. 

While calculating yardage needed is a little more time consuming it’s no more difficult. For the rectangle quilt at the top of the page, I’m using leftover strips and fat quarters but it would be easy to calculate what I needed. I do have a fabric calculator but most of the time I find it easier to just calculate how many pieces I can get from a strip and how many strips I need to get all the pieces for my block. It does come in handy when I’m trying to figure out how much yardage I need for simple squares or how many binding strips I need to cut. 

Suppose I was starting with 2.5 inch strips and planned to use a single fabric for the background. 

First up, I’d decide how big I wanted my quilt. I love using 8 inch blocks for these small child size quilts because a 5×7 set works out well for me to quilt here on my regular sewing machine, and at 40 x 56 inches it fits on a baby size package batting. 

Next – my rectangles are 2.5 x 4.5 inches so I calculate how many sections I can get from one strip. Since fabric widths vary I use 40 inches in my calculations. 

40 divided by 4.5 = 8.88 

I need 4 rectangles for each block so I know that each strip will make 2 blocks. 

I need 35 blocks divided by 2 since each strip is going to make 2 blocks = 17.5 strips

I choose 18 different fabrics – this is where a jelly roll would be nice for my colored rectangles 

To calculate how much background fabric I need 

18 strips x 2.5 inches = 45 inches of fabric

Since there are 36 inches of fabric in a yard, I divide 45 by 36 and see that I need 1 and a quarter yards of my background fabric plus I’d add in a few extra inches to straighten the edge of my fabric and in case I miss cut something. 

To make this easier to piece, I’d sew a colored strip to a background strip and then subcut my sections into 4.5 inches. 

I know this doesn’t make exciting reading but maybe someone will stop and realize they can do their own math before writing me to ask me to do it for them!! 

8 thoughts on “Rectangles, leftovers, & quilt math

  1. Penny G

    I have enough comfort with math to figure out how much fabric to make a quilt larger, or how many extra blocks. Some people see a quilt and just don’t get how to modify. It is not stupidity or laziness, it is just something in how their mind works. I use the ratios in your strippie quilt to make many different sizes. The different sizes are generally driven by my buying some remnant and trying to get a cute quilt in a usable size. I add borders so often because adults love the pattern. I tried to explain to my daughter what I was doing. She is intelligent and successful, but has no idea what I am saying when I try to explain sizing a quilt. I also talked about making a quilt from left over blocks – eyes glazed. The other daughter helped create a cute layout. Minds just don’t work the same.

  2. Joanne Hubbard

    I too like rectangle quilts and think yours look great. For me, the visual impact of rectangles versus squares is really fun and much more exciting. 🙂

    I teach a lot of quilt classes and find that the most asked questions in EVERY class deal with math. I am often asked about resizing a block or determining how many blocks I need for a specific size quilt. There are also a lot of questions about fabric requirements, especially if they are adding a border that isn’t used in the original pattern. Fabric requirements for binding or side setting triangles are common concerns as well. I’ve offered a Math for Quilters class, but generally don’t get many people to sign up for it. I was told that it’s much easier to simply buy extra fabric instead of doing the math. I get that, but since I’m trying to reduce my stash that would not work for me. 🙂

  3. Elaine/MuddlingThrough

    Isn’t it fun using leftovers! It seems like a free quilt to me. I really like all of these you’re showing today, but especially the batik windmills. I can see one of those happening here soon! Thank you for sharing all your wonderful ideas!

  4. Judy

    I really like the windmill quilt also. I think it would make a great scrap quilt.
    I do a little teaching of quilt making and am always amazed at how few people can do their own quilt math. And have no interest in learning.

  5. Bonnie in Va

    Nothing wrong with a little math lesson! I often start a quilt with not set size in mind and make decisions as I go along. Not the best way. Sometimes (but not all that often) I’ll cut everything out before I actually start sewing. Not my favorite but sometimes it needs to be done. Thanks for sharing all of your lovely strip quilts.

  6. Susie Q

    May not be exciting reading but some may realize they can do their own calculations. And it gives us a reason to tell high school kids where they can use geometry.

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