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Thread: Could someone explain something to me, please?

  1. #1
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    Could someone explain something to me, please?

    I have been reading an article about organizing your stash and came across a line that said, basicallly- a finished square is 1/2 inch smaller than the original cut square. So if I have a 4 inch square, taken out of my red box, after sewing it to other squares, it should measure 3 1/2 inches - that is using 1/4 inch seam allowance. The accompanying illustration has the original square attached on all 4 sides.

    ****Why is the finished square only 3.5 inches and not 3 inches if you are sewing all 4 sides using a 1/4 inch seam allowance? After all, you are taking 1/4 inch off all 4 sides and 1/4+1/4+1/4+1/4=1***

    I know math is not my strong suit, but am I that weak in it?

    thank you so much! the things you think about when you have insomnia

    Debbie

  2. #2
    Super Member katesnanna's Avatar
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    Because you only take 1/2inch from the length and 1/2 inch from the width.

  3. #3
    Super Member virtualbernie's Avatar
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    Because you are only taking 1/4" off EACH of the 4 sides. left and right, top and bottom.
    Bernie

  4. #4
    Super Member sandyl's Avatar
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    OH, I love this! This is indeed something that would keep me awake nights, too. It sure makes sense that 1/4 x 4 is 1. But when you split them up (1/4 on each side) it does boggle my mind, too. ......I hate math and always have-I usually call in help (DH).

  5. #5
    Senior Member happyquiltmom's Avatar
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    Try it on a scrap of fabric and you'll get a visual of why it is true. You take 1/4" off the left, and 1/4" off the right, which adds up to 1/2" horizontally. Then you take 1/4" off the top and 1/4" off the bottom for a total of 1/2" vertically. So, your 4" square ends up being 3 1/2" at the end.

  6. #6
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    A similar case happened to me many years ago about the 7/8" added to a triangle.
    I had to cut a square - say 6", then divide it diagonally into a triangle, then add the 1/4" all around and then measure the base to the tip of the diagonal line. It was 6 7/8". Then it all came clear to me.

  7. #7
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    Quote Originally Posted by Holice View Post
    A similar case happened to me many years ago about the 7/8" added to a triangle.
    I had to cut a square - say 6", then divide it diagonally into a triangle, then add the 1/4" all around and then measure the base to the tip of the diagonal line. It was 6 7/8". Then it all came clear to me.
    This is the one I had to draw out for myself, too.
    Attached Images Attached Images

  8. #8
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    Yeah the 7/8 was confusing for me too. Once I drew it out i became clear.

  9. #9
    Super Member Nanamoms's Avatar
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    This reminds me of my sister and I calculating measurements for an isolette cover. She's a nurse and I do accounting. We both calculate things in opposite ways. We just cracked up laughing while laying out our measurements...To hear us "arguing" over how to do it and both of us said this isn't rocket science!!

  10. #10
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    First, thank you for the responses... I'm coming to the conclusion this is something I just need "to do" and not think about. if I need a certain size finished square, I just need to cut the fabric 1/2 inch larger than I need for I am taking a 1/2 inch off the width and length. If I need 1/2 square triangles, I need to add 7/8"... (going to make a cheat sheet at home)...

    but I just can't get my head around the reasoning (tell ya, I'm not good at math reasoning) if I taking a 1/4 inch off each side (1/2 " total for width and 1/2" total for length) that still gives me 1" taken off for seam allowances. why isn't that calculated- for 1/2 off width + 1/2 off length = 1").

    ugh. guess there are some things I will never understand and that's why we have cheat sheets.... but now I know why my current quilt has gotten wonky...

    thank you! :

  11. #11
    Super Member justflyingin's Avatar
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    Things can get tricky when you are dealing with measurements for quilting. So, don't be ashamed to draw things out, use cheat sheets or simply ask here....people are always willing to help.

  12. #12
    Super Member mom-6's Avatar
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    Hey, don't feel bad! I 'thought' I was pretty good at math till I started quilting - have discovered otherwise...
    legendarycandles.com
    Just discovered I qualify for FABLE (Fabric Acquired Beyond Life Expectancy)

  13. #13
    Power Poster MadQuilter's Avatar
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    Your piece of fabric has two directions: width and length. In case of a square, these dimensions are the same.

    Let's use a rectangle as an example, maybe that will make more sense. Let's say the size of the fabric rectangle is 3" by 5" - Now you sew another rectangle to the first one along the 5" measurement. You will use 1/4" seam on BOTH pieces and both rectangles will be 2 3/4" x 5". Sew another rectangle to the bottom and now your center piece will be 2 1/2" x 5" (Notice how the 5" measurement has not changed yet).

    Now imagine that you sew a 3" x 5" piece to the end. This will leave each piece at 3" x 4 3/4" Sew the other piece to the other end and your center patch will be 3" x 4 1/2" (Notice how the 3" measurement hasn't changed)

    If you sew pieces all around then you will use up 1/4" on the top, and 1/4" on the bottom (and this measurement will be subtracted from the height). Then you will use up 1/4" on the left side and 1/4" from the right side (and this measurement will be subtracted from the width).
    Martina
    Life, Liberty, and the Pursuit of Fabric!

  14. #14
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    Because you're taking the same 1/4 inch off the top and bottom as you're taking off the sides. You can't add it up.ha.

  15. #15
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    Tricky for a lot of people huh!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  16. #16
    Super Member paulswalia's Avatar
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    Think of it this way, a 3.5 in square is that measurement ACROSS the square, not 3.5 across plus 3.5 top to bottom, so you only take off the quarter inch seam two times, because that is what affects the measurement across the square. Does that help? Your plan for a cheat sheet is a good one. I copied one from a magazine a long time ago and it lives by my machine.

  17. #17
    Super Member ghostrider's Avatar
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    Quote Originally Posted by callie8799 View Post
    but I just can't get my head around the reasoning (tell ya, I'm not good at math reasoning) if I taking a 1/4 inch off each side (1/2 " total for width and 1/2" total for length) that still gives me 1" taken off for seam allowances. why isn't that calculated- for 1/2 off width + 1/2 off length = 1").
    Come at it from the other way. Your 4" cut square is 4" wide by 4" high...or 8" total if you combine them. If you then subtract the 1" of seam allowances, you get 7". Divide that in half (because it's a square and length and width are the same) and you get a 3" square. Does that help you see it?

    If you consider both directions (length and width) for one element (the seam allowances), you have to do it for the other as well (the square sides).
    Last edited by ghostrider; 05-24-2012 at 05:03 AM.
    The Earth without art is just "Eh".

  18. #18
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    I understand the math, and I understand the confusion. Sometimes you just have to believe and take that leap of faith and cut the way the other quilters say to cut. Understanding will come when you cut and sew. In my case, understanding comes slowly....thank you patient quilting community!

  19. #19
    Super Member Latrinka's Avatar
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    Sometimes you just have to Not think too much! LOL!
    If a woman's work is never done....why start?

  20. #20
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    I so agree that overthinking can be your worst enemy!!
    Penny aka PLS 1946

  21. #21
    Super Member SunlitenSmiles's Avatar
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    because you are working with a square not a straight line.......not arithmatic it is geometry...pardon my spelling

  22. #22
    Super Member Treasureit's Avatar
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    I get the math, but my reality is that no matter how I measure it...after I "sew" it....3 1/2 can be more or less...depending on my sewing skills for the day! LOL

  23. #23
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    I LOVE this thread! I get all wound up in trying to understand stuff like this and have to draw diagrams too. The REALLY funny part is that I am a statistician and I have been TEACHING statistical analysis at various universities for 40 years! But it's a different kind of math. You would not believe the scrapes I've gotten myself into with "quilting math" -- especially when someone else asks me questions because they assume that I must be an expert!

  24. #24
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    It takes 1" off the area, not the linear measurements. Right?
    Judy

  25. #25
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    No. Wrong. It takes more than that off the area. Strange thing, math.
    Judy

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